Lighting system

ABSTRACT

Semiconductor light-emitting devices are provided. The semiconductor light-emitting devices include a substrate and a crystal layer selectively grown thereon at least a portion of the crystal layer is oriented along a plane that slants to or diagonally intersect a principal plane of orientation associated with the substrate thereby for example, enhancing crystal properties, preventing threading dislocations, and facilitating device miniaturization and separation during manufacturing and use thereof.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/062,687, filed on Jan. 30, 2002, now U.S. Pat. No.6,924,500, the disclosure of which is herein incorporated by reference,which is a continuation of International Application No. PCT/JP01/06212with an international filing date of Jul. 18, 2001, and which claimspriority to Japanese Patent Application No. P2000-218034 filed on Jul.18, 2000; Japanese Patent Application No. P2000-217663 filed on Jul. 18,2000; Japanese Patent Application No. P2000-217508 filed on Jul. 18,2000; Japanese Patent Application No. P2000-217799 filed on Jul. 18,2000; Japanese Patent Application No. P2000-218101 filed on Jul. 18,2000; and Japanese Patent Application No. P2001-200183 filed on Jun. 29,2001, the above-referenced disclosures of which are herein incorporatedby reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to semiconductor devices. Morespecifically, the present invention relates to semiconductorlight-emitting devices and processes for producing same.

Among known semiconductor light-emitting devices is one which consistsof a low-temperature buffer layer, an n-side contact layer of Si-dopedGaN, an n-side cladding layer of Si-doped GaN, an active layer ofSi-doped InGaN, a p-side cladding layer of Mg-doped AlGaN, and a p-sidecontact layer of Mg-doped GaN, which are sequentially formed on top ofthe other over the entire surface of a sapphire substrate. Commercialproducts of such structure, available in large quantities, are blue andgreen LEDs (Light-Emitting Diodes) which emit light with wavelengthsranging from 450 nm to 530 nm.

Growing gallium nitride crystal on a sapphire substrate is a commonpractice. The sapphire substrate used for this purpose is usually onewhich has the C-plane (i.e., the (0001) plane in accordance with Millerindices of a hexagonal crystal system) as the principal plane.Consequently, the gallium nitride layer formed on the principal planealso has the C-plane, and the active layer, which is formed parallel tothe principal plane of the substrate, and the cladding layers holdingthe active layer between them are also parallel to the C-plane. Thesemiconductor light-emitting device having crystal layers sequentiallyformed on the basis of the principal plane of the substrate has a smoothsurface desirable for the formation of electrodes, due to the smoothnessof the principal plane of the substrate.

A disadvantage of growing gallium nitride on a sapphire substrate isthat dislocations may densely exist in the crystals due to latticemismatch between them. Attempts have been made to eliminate defects inthe grown crystals by forming a low-temperature buffer layer on thesubstrate. Japanese Patent Laid-open No. Hei 10-312971 discloses thecombination with epitaxial lateral overgrowth (ELO) for reduction incrystal defects.

Also, Japanese Patent Laid-open No. Hei 10-321910 discloses asemiconductor light-emitting device, wherein the light-generating regionextends vertically to the principal plane of the substrate in ahexagonal prismatic structure which is formed on the substrate such thatits (10—10) or (1–100) M-plane is vertical (i.e., substantiallyperpendicular) to the principal plane of the substrate. The activelayer, vertical to the principal plane of the substrate, is known to beeffective in suppressing defects and dislocations due to latticemismatch with the substrate and reducing strain due to difference in thecoefficient of thermal expansion.

Moreover, Japanese Patent Laid-open No. Hei 8-255929 discloses a processfor producing a light-emitting device. The process consists of forming,on a substrate, a layer of gallium nitride compound semiconductor of oneconductivity type, covering part of the layer with a mask, forming, onthe uncovered part, a layer of gallium nitride compound semiconductor(including a layer of another conductivity type) by selective growth,and forming a p-electrode and an n-electrode.

The technique of forming a hexagonal prismatic structure vertical to theprincipal plane of the substrate as disclosed in Japanese PatentLaid-open No. Hei 10-321910 requires that the film obtained by HVPE(hydride vapor phase epitaxy) should be followed by dry etching to givethe (10—10) or (1–100) M-plane. Unfortunately, dry etching inevitablydamages the crystal face. In other words, dry etching deteriorates thecharacteristic properties of crystals despite its effect of suppressingthreading dislocations from the substrate. Further, an additionalproduction step or process stage is required to perform dry etching.

It is known that selective growth on the C+-plane of the sapphiresubstrate gives a crystal layer with sharp peaks surrounded by the(1–101) plane or the S-plane (See Japanese Patent No. 2830814, paragraph0009 of specification). The layer thus obtained is not flat enough forthe electrode to be formed thereon. Therefore, it has never been usedfor electronic devices and light-emitting devices, and is merely used asan underlying layer of crystal structure for further selective growth.

Any device having a surface parallel to the principal plane of thesubstrate needs a flat surface for good crystal properties. As theresult, it is usually constructed such that the electrodes spreadhorizontally. A disadvantage of this structure is that the horizontallyspread electrodes make for extremely difficult and time-consuming workbecause one must separate miniature chips without cutting thehorizontally spread electrodes. Moreover, the sapphire substrate andnitride (such as GaN) are so hard that they are difficult to cut andrequire a cutting allowance of about 20 μm (i.e., micrometers), therebymaking it even more difficult to cut the miniature chips.

Additionally, a problem with a light-emitting device in which theprincipal plane of the substrate is a C+-plane and the active layer ofgallium nitride is formed parallel to the principal plane of thesubstrate is that there is only one bond from gallium atoms to nitrogenatoms in the C+-plane and hence, nitrogen atoms easily dissociate fromthe crystal face of the C+-plane, thereby making it difficult for theeffective V/III ratio to be large, which in turn prevents improvement inperformance of crystals constituting the light-emitting device.

The technology disclosed in Japanese Patent Laid-open No. Hei 8-255929has an advantage of using selective growth which obviates the necessityof etching, such as reactive ion etching. However, it presentsdifficulties in forming the n-electrode accurately because largeproduction steps occur in its vicinity after the mask layer has beenremoved. A disadvantage of forming the active layer parallel to theprincipal plane of the substrate, as in the light-emitting devicedisclosed in Japanese Patent Laid-open No. Hei 8-255929, is that the endof the active layer is exposed to air, thereby resulting in oxidationand deterioration of the active layer.

It is known that an LED device can be used as a light source for largedisplay (such as projection display). To this end, it is important forLED devices to have higher brightness, better reliability, and lowerproduction costs. The brightness of LED devices is governed by twofactors: the internal quantum efficiency, which depends on the crystalproperties of the active layer; and the light emergence efficiency,which is a ratio of light which has escaped from the device to lightwhich has been generated in the device.

In general, a light-emitting diode has a light-generating region, thetypical structure of which is shown in FIG. 1. The major parts of thelight-generating region include an active layer 400 of, typically,InGaN, a first conductive layer 401 and a second conductive layer 402(which hold the active layer 400 between them), and a reflecting film403 (which also functions as an electrode) on the second conductivelayer 402 opposite to the active layer 400, with the interface betweenthe reflecting film 403 and the second conductive layer 402 functioningas a reflecting plane 404. Part of the light generated by the activelayer 400 emerges directly from the light emerging window 405 in thefirst conductive layer 401, and part of the light advancing toward thesecond conductive layer 402 is reflected by the reflecting plane 404 andthe reflected light advances toward the light emerging window 405 in thefirst conductive layer 401.

A disadvantage of the above-mentioned light-emitting diode of ordinarystructure is that light generated by the active layer 400, howeverefficient it might be, cannot be extracted from the device due to totalreflection that takes place at an interface between the device and theoutside, between the device and the transparent substrate, and/orbetween the transparent substrate and the outside. In other words, lightincident to the interface at an angle smaller than the critical angle issubject to total reflection. The critical angle depends on therefractive indices of the two materials forming the interface. In thelight-emitting diode of surface emitting type which has the reflectingplane 404 and the light emerging window 405 parallel to each other asshown in FIG. 1, the light which has undergone total reflection at anangle smaller than the critical angle undergoes total reflectioncontinuously between the reflecting plane 404 and the light emergingwindow 405. Hence, such light cannot be extracted as an effectiveoutput.

Attempts have been made to improve light emergence efficiency by forminga convex or a slope which changes the optical path in the device, sothat the convex or slope functions as the reflecting plane which permitslight to emerge efficiently. This technique, however, is not readilyapplicable to the GaN semiconductor which is used for blue or greenLEDs. At present, it is believed that forming a sophisticated shape inan extremely small region is not known.

A sectional view of a light-emitting device of surface emitting type isshown in section in FIG. 2. It is formed on a substrate for growth 500of sapphire. On the substrate 500 are sequentially formed a firstconductive layer 501 of gallium nitride semiconductor, an active layer502 of gallium nitride semiconductor, and a second conductive layer 503of gallium nitride semiconductor, all parallel to the principal plane ofthe substrate. The active layer 92 and the second conductive layer 503are partly removed such that an opening 506, whose bottom penetratesinto the first conductive layer 501, is formed. In the opening 506, afirst electrode 504 is formed such that it connects to the firstconductive layer 501. A second electrode 505 is formed on the secondconductive layer 503, thereby connecting to the second conductive layer503.

A simple way to meet requirements of the light source for large displaysis to increase the device size according to the desired brightness.However, the optical design limits the size of the light-generatingregion, which presents difficulties in producing a device having highbrightness as well as a large light-generating region. Moreover, theactive region in the device is also limited by the arrangement of thelight emerging window and the electrodes for efficient currentinjection. At present, therefore, the requirement for high brightness ismet by injecting more than the specified current into the actual device.However, increased current injection impairs device reliability.

On the other hand, decreasing the device size of light-emitting diode isexpected to reduce production cost through improvement in yields. Thereis a strong demand for size reduction in the area where LEDs in an arrayhaving individual pixels for display. However, size reduction leads toan increased load per unit area, which contradicts the above-mentionedrequirements for high brightness and high reliability.

Moreover, if the device size is to be reduced below tens of micrometersor less, the region for the active layer is greatly limited by theelectrodes 504 and 505 (shown in FIG. 2) and the device separatinggrooves. The region where the conductive layers 503 and 501 come intocontact with the electrodes 505 and 504 should be as large as possibleto keep resistance low. However, enlarging the electrodes reduces thearea through which light emerges from the active region, which leads toreduced brightness.

A need, therefore, exists to provide a micro-size light-emitting devicewith efficient light emergence, high brightness, minimum load on theactive layer and controlling threading dislocations from the substratethat can be produced under optimal process conditions.

SUMMARY OF THE INVENTION

The present invention relates to semiconductor light-emitting devicesand methods of producing same. The light-emitting devices of the presentinvention include a crystal structure formed by selective growth andoriented about a crystal plane with respect to a substrate such that thelight-emitting properties can be enhanced.

Applicants have discovered that the light-emitting devices of thepresent invention can be produced, for example, under optimal processconditions, such as, without requiring additional production steps orprocess stages, by controlling threading dislocations from the substrateand maintaining desirable crystal properties, thereby also protectingthe active layer from deterioration. In this regard, the light-emittingdevices of the present invention are desirably reliable with minimumload on the active layer (e.g., light-generating region) and can providean enhanced level of brightness due to, for example, the improved lightemergence efficiency.

To this end, in an embodiment of the present invention, a semiconductorlight-emitting device is provided. The semiconductor light-emittingdevice includes a substrate including a substrate surface positionedalong a substrate surface plane, a crystal layer having a crystalsurface oriented along a crystal surface plane diagonally intersectingthe substrate surface plane, and a first conductive layer, an activelayer, and a second conductive layer each formed along at least aportion of the crystal surface.

In an embodiment, the crystal layer is a wurtzite crystal structure.

In an embodiment, the crystal layer is composed of a nitridesemiconductor material.

In an embodiment, the crystal layer is formed by selective growth on thesubstrate with a material layer capable of growth interposedtherebetween.

In an embodiment, the material layer capable of growth is selectivelyremoved during selective growth to form the crystal layer.

In an embodiment, the semiconductor light-emitting device furtherincludes a masking layer having an opening through which the crystallayer is selectively grown.

In an embodiment, the crystal layer is formed by selective growth suchthat the crystal layer extends laterally from the opening in the maskinglayer.

In an embodiment, the substrate plane is a C-plane.

In an embodiment, the crystal surface plane includes at least one of aS-plane and a (11–22) plane.

In an embodiment, the crystal surface plane includes a plane having aplane orientation inclined at an angle ranging from about 5 to about 6degrees with respect to at least one of a S-plane and a (11–22) plane.

In an embodiment, current is injected into the active layer.

In an embodiment, active layer includes InGaN.

In an embodiment, the crystal layer is a substantially symmetricalhexagonal structure.

In an embodiment, a portion of the crystal surface is oriented along aC-plane and positioned centrally along the crystal structure withrespect to a second portion of the crystal surface that is orientedalong the crystal surface plane which diagonally intersects thesubstrate surface plane.

In another embodiment according to the present invention, an imagedisplay unit is provided. The image display unit includes a number ofsemiconductor light-emitting devices arranged so as to emit light inresponse to a signal, each of the semiconductor light-emitting deviceshaving a substrate including a substrate surface positioned along asubstrate surface plane, a crystal layer including a crystal surfaceoriented along a crystal surface plane diagonally intersecting thesubstrate surface plane, and a first conductive layer, an active layer,and a second conductive layer each formed along at least a portion ofthe crystal surface.

In yet another embodiment according to the present invention, a lightingsystem is provided. The lighting system includes a number ofsemiconductor light-emitting devices, each of the semiconductorlight-emitting devices having a substrate including a substrate surfacepositioned along a substrate surface plane, a crystal layer including acrystal surface oriented along a crystal surface plane diagonallyintersecting the substrate surface plane, and a first conductive layer,an active layer, and a second conductive layer each formed along atleast a portion of the crystal surface.

In an embodiment, each of the semiconductor light-emitting devices inthe lighting system are arranged so as to emit light in response to anidentical signal.

In a further embodiment according to the present invention, a processfor producing a semiconductor light-emitting device is provided. Theprocess includes the steps of providing a substrate including asubstrate surface oriented along a substrate surface plane, forming acrystal seed layer on the substrate surface, forming a masking layer onthe crystal seed layer, wherein the masking layer includes an opening,forming a crystal layer by selective growth of the crystal seed layerthrough the opening of the masking layer, wherein the crystal layerincludes a crystal layer surface oriented along a crystal layer planethat diagonally intersects the substrate surface, and forming each of afirst conductive layer, an active layer, and a second conductive layeralong at least a portion of the crystal layer surface.

In an embodiment, the substrate surface plane comprises a C-plane.

In an embodiment, the process for producing a semiconductorlight-emitting device further includes the step of forming a number ofsemiconductor light-emitting devices spaced apart along the substrate.

In an embodiment, the process for producing a semiconductorlight-emitting device further includes the step of forming an electrodeon at least a side of each semiconductor light-emitting device.

According to an embodiment of the present invention, a semiconductorlight-emitting device is provided. The semiconductor light-emittingdevice includes a substrate including a substrate surface positionedalong a substrate surface plane, a crystal layer having a crystal layersurface oriented along a crystal surface plane defined as a S-planewhich diagonally intersects the substrate surface plane, and a layer ofa first conductivity type, an active layer, and a layer of a secondconductivity type each formed along the S-plane.

In an embodiment, the crystal layer is a wurtzite crystal structure.

In an embodiment, the crystal layer is composed of a nitridesemiconductor material.

In an embodiment, the crystal layer is formed by selective growth on thesubstrate with a material layer capable of growth interposedtherebetween.

In an embodiment, the material layer capable of growth is selectivelyremoved during selective growth to form the crystal layer.

In an embodiment, the semiconductor light-emitting further includes amasking layer having an opening through which the crystal layer isselectively grown.

In an embodiment, the crystal layer is formed by selective growth suchthat the crystal layer extends laterally from the opening in the maskinglayer.

In an embodiment, the substrate surface plane comprises a C+ plane.

In an embodiment, current is injected into the active layer.

According to yet another embodiment of the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate including a substrate surfacepositioned along a substrate surface plane, a crystal layer in the shapeof approximately hexagonal pyramid and having a face oriented along anS-plane that diagonally intersects the substrate surface plane, and alayer of a first conductivity type, an active layer, and a layer of asecond conductivity type each formed along at least a portion of theapproximately hexagonal pyramid.

In an embodiment, current is injected into the active layer such that acurrent density is lower near or at an apex of the approximatelyhexagonal pyramid than in the face of the approximately hexagonalpyramid.

According to a further embodiment of the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate including a substrate surfacepositioned along a substrate surface plane, a crystal layer in the shapeof an approximately hexagonal prismoid, having a face oriented about anS-plane, and a top region oriented about a C-plane, and a layer of afirst conductivity type, an active layer, and a layer of a secondconductivity type each formed along at least a portion of theapproximately hexagonal prismoid.

According to yet another embodiment of the present invention, an imagedisplay unit in provided. The image display unit includes a number ofsemiconductor light-emitting devices arranged so as to emit light inresponse to a signal, each of the semiconductor light-emitting deviceshaving a substrate including a substrate surface positioned along asubstrate surface plane, a crystal layer having a crystal surfaceoriented along a crystal surface plane defined as a S-plane whichdiagonally intersects the substrate surface plane, and a firstconductive layer, an active layer, and a second conductive layer eachformed along at least a portion of the crystal surface.

In an embodiment according to the present invention, a lighting systemis provided. The lighting system includes a number of semiconductorlight-emitting devices, each of the semiconductor light-emitting deviceshaving a substrate including a substrate surface positioned along asubstrate surface plane, a crystal layer having a crystal surfaceoriented along a crystal surface plane defined as a S-plane whichdiagonally intersects the substrate surface plane, and a firstconductive layer, an active layer, and a second conductive layer eachformed along at least a portion of the crystal surface.

In an embodiment, each of the semiconductor light-emitting devices inthe lighting system are arranged so as to emit light in response to anidentical signal.

In yet another embodiment according to the present invention, a processfor producing a semiconductor light-emitting device is provided. Theprocess includes the steps providing a substrate including a substratesurface oriented along a substrate surface plane, forming a maskinglayer on the substrate, wherein the masking layer includes an opening,forming a crystal layer by selective growth through the opening of themasking layer, wherein the crystal layer includes a crystal layersurface oriented along a crystal layer plane defined as a S-plane whichdiagonally intersects the substrate surface plane, and forming each of afirst conductive layer, an active layer, and a second conductive layeralong at least a portion of the crystal layer surface.

In an embodiment, the substrate surface plane is a C+ plane.

In an embodiment, the process for producing a semiconductorlight-emitting device further includes the steps of forming a number ofthe semiconductor light-emitting devices on the substrate, andsubsequently separating the semiconductor light-emitting devices.

In an embodiment, each separated semiconductor light-emitting device hasat least one electrode formed on a side.

In a further embodiment according to the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate having a substrate surfacepositioned along a substrate surface plane, a crystal grown layer formedby selective growth having a crystal surface oriented along a crystalsurface plane diagonally intersecting the substrate surface plane, anactive layer which is formed along at least a portion of the crystalgrown layer that emits light upon injection of an amount of current, anda reflecting region which is formed substantially parallel to thecrystal surface plane and reflects at least a portion of the lightemerging from the active layer.

In an embodiment, the active layer is formed from a compoundsemiconductor having a wurtzite crystal structure.

In an embodiment, the active layer is approximately parallel to thecrystal surface plane.

In an embodiment, the active layer is approximately parallel to aS-plane.

In an embodiment, the active layer is approximately parallel to a planehaving a plane orientation inclined at an angle ranging from about 5 toabout 6 degrees with respect to at least one a S-plane and a (11–22)plane.

In an embodiment, the reflecting region includes at least two reflectingplanes that intersect at an angle less than 180°.

In an embodiment, the active layer is formed from a nitride compoundsemiconductor.

In an embodiment, the active layer is formed from a gallium nitridecompound semiconductor.

In an embodiment, the active layer contains In.

In an embodiment, the active layer is separated for each device.

In an embodiment, the semiconductor light-emitting device furtherincludes an underlying layer formed on the substrate, wherein theselective growth of the crystal grown layer is derived from theunderlying layer.

According to an embodiment of the present invention a process forproducing a semiconductor light-emitting device is provided. The processincludes the steps of providing a substrate including a substratesurface oriented along a substrate surface plane, selectively growing acrystal layer having a crystal surface oriented along a crystal surfaceplane diagonally intersecting the substrate surface plane, forming anactive layer approximately parallel to the crystal surface plane, andforming a reflecting region substantially parallel to the crystalsurface plane.

According to another embodiment of the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate having a substrate surfaceoriented along a substrate surface plane, a first grown layer having afirst grown layer conductivity type formed on the substrate, a maskinglayer formed on the first grown layer, a second grown layer of a secondgrown layer conductivity type formed by selective growth through anopening in the masking layer having a crystal surface oriented along acrystal surface plane, a first cladding layer including a first claddinglayer conductivity type formed along at least a portion of the crystalsurface plane, an active layer, and a second cladding layer including asecond cladding layer conductivity type, wherein at least one of thefirst cladding layer, the active layer, and the second cladding layercover the masking layer surrounding the opening.

In an embodiment, the first grown layer conductivity type, the secondgrown layer conductivity type, and the first cladding layer conductivitytype are all of a first conductivity type and the second cladding layerconductivity type is of a second conductivity type.

In an embodiment, the crystal surface plane of the second grown layerdiagonally intersects the substrate surface plane.

In an embodiment, the first and second grown layers are composed of awurtzite crystal structure.

In an embodiment, the second grown layer is composed of a nitridesemiconductor.

In an embodiment, the substrate surface plane is a C-plane.

According to yet another embodiment of the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate, a first grown layerincluding a first grown layer conductivity type formed on the substrate,a masking layer formed on the first grown layer, a second grown layerincluding a second grown layer conductivity type formed by selectivegrowth through an opening in the masking layer and having a crystalsurface oriented along a crystal surface plane, a first cladding layerincluding a first cladding layer conductivity type formed along at leasta portion of the crystal surface plane, an active layer, and a secondcladding layer including a second cladding layer conductivity type,wherein the first cladding layer, the active layer, and the secondcladding layer are formed as to substantially cover the second grownlayer.

In an embodiment, the first grown layer conductivity type, the secondgrown layer conductivity type, and the first cladding layer conductivitytype are all composed of a first conductivity type while the secondcladding layer conductivity type is composed of a second conductivitytype.

According to still another embodiment of the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate, a first grown layer of afirst grown layer conductivity type formed on the substrate, a maskinglayer formed on the first grown layer, a second grown layer of a secondgrown layer conductivity type formed by selective growth through anopening in the masking layer and including a crystal surface orientedalong a crystal surface plane, a first cladding layer of a firstcladding layer conductivity type formed along at least a portion of thecrystal surface plane, an active layer, and a second cladding layer of asecond cladding layer conductivity type, wherein the first claddinglayer, the active layer, and the second cladding layer are formedsubstantially parallel to the crystal surface plane such that an endregion of at least one of the first cladding layer, the active layer,and the second cladding layer contacts the masking layer.

In an embodiment, the first grown layer conductivity type, the secondgrown layer conductivity type, and the first cladding layer conductivitytype are all of a first conductivity type while the second claddinglayer conductivity type is of a second conductivity type.

In an embodiment according to the present invention, an image displayunit is provided. The image display unit includes a number ofsemiconductor light-emitting devices arranged so as to emit light inresponse to a signal, each of the semiconductor light-emitting deviceshaving a substrate, a first grown layer of a first conductivity typeformed on the substrate, a masking layer formed on the first grownlayer, a second grown layer of the first conductivity type formed byselective growth through an opening in the masking layer and including acrystal surface oriented along a crystal surface plane, a first claddinglayer of the first conductivity type formed along at least a portion ofthe crystal surface plane, an active layer, and a second cladding layerof a second conductivity type, wherein the first cladding layer, theactive layer, and the second cladding layer are formed substantiallyparallel to the crystal surface plane such that an end region of atleast one of the first cladding layer, the active layer, and the secondcladding layer extends to the masking layer in proximity to the opening.

In another embodiment according to the present invention, a lightingsystem is provided. The lighting system includes a number ofsemiconductor light-emitting devices, each of the semiconductorlight-emitting devices having a substrate, a first grown layer includinga first conductivity type formed on the substrate, a masking layerformed on the first grown layer, a second grown layer including thefirst conductivity type formed by selective growth through an opening inthe masking layer and including a crystal surface oriented along acrystal surface plane, a first cladding layer including the firstconductivity type formed along at least a portion of the crystal surfaceplane, an active layer, and a second cladding layer of a secondconductivity type, wherein the first cladding layer, the active layer,and the second cladding layer are formed substantially parallel to thecrystal surface plane such that an end region of at least one of thefirst cladding layer, the active layer, and the second cladding layerextends to the masking layer in proximity to the opening.

In an embodiment, the lighting system is configured such that each ofthe semiconductor light-emitting devices are arranged so as to emitlight in response to an identical signal.

According to yet another embodiment of the present invention, a processfor producing a semiconductor light-emitting device is provided. Theprocess includes the steps of providing a substrate including asubstrate surface oriented along a substrate surface plane, forming afirst grown layer on the substrate, forming a masking layer having anopening on the first grown layer, selectively growing a second grownlayer through the opening in the masking layer, wherein the second grownlayer includes a crystal surface oriented along a crystal surface plane,and forming a cladding layer of a first conductivity type, an activelayer, and a cladding layer of a second conductivity type eachsubstantially parallel to the crystal surface plane extending to themasking layer in proximity to the opening.

In an embodiment, the crystal surface plane of the second grown layerdiagonally intersects the substrate surface plane.

According to a further embodiment of the present invention, asemiconductor light-emitting device is provided. The semiconductorlight-emitting device includes a substrate having a substrate surfaceoriented along a substrate surface plane, and an active layer formedalong at least a portion of a selectively grown crystal layer via awindow region along the substrate surface plane such as to be disposedbetween a first conductive layer and a second conductive layer andoriented along an active layer plane that is not parallel to thesubstrate surface plane, and wherein an area of the active layer islarger than at least one of an area of the window region and a projectedarea of the crystal layer derived from projecting the crystal layer tothe substrate surface plane in a normal direction.

In an embodiment, the active layer is composed of a compoundsemiconductor having a wurtzite crystal structure.

In an embodiment, the active layer is substantially parallel to aS-plane.

In an embodiment, the active layer is formed such that it extendslaterally from the window region.

In an embodiment, the semiconductor light-emitting device furtherincludes a first electrode connected to the first conductive layer, anda second electrode connected to the second conductive layer, wherein thefirst electrode and second electrode are capable of injecting currentinto the active layer.

In an embodiment, the active layer is a nitride compound semiconductor.

In an embodiment, the active layer is a gallium nitride compoundsemiconductor.

In an embodiment, the active layer contains In.

In an embodiment, the semiconductor light-emitting device furtherincludes a number of semiconductor light-emitting devices selectivelygrown such that the active layer of each semiconductor light-emittingdevice is separated from the active layer of adjacent semiconductorlight-emitting devices.

In an embodiment, the selective growth is derived from an underlyinglayer formed on the substrate.

According to an embodiment of the present invention, a semiconductorlight-emitting device is provided. The semiconductor light-emittingdevice includes a substrate having a substrate surface oriented along asubstrate surface plane, and an active layer formed by selective growthsuch as to be disposed between a first conductive layer and a secondconductive layer and oriented along an active layer plane that is notparallel to the substrate surface plane, and wherein a portion of theactive layer is directed away from the active layer plane towards thesubstrate.

According to yet an embodiment of the present invention, a semiconductorlight-emitting device is provided. The semiconductor light-emittingdevice includes a substrate including a substrate surface oriented alonga substrate surface plane, and an active layer formed along at least aportion of a selectively grown crystal layer such as to be disposedbetween a first conductive layer and a second conductive layer andoriented along an active layer plane that is not parallel to thesubstrate surface plane, and wherein an area of the active layer greaterthan or equal to a sum of a projected area of the crystal layer derivedfrom projecting the crystal layer to the substrate in a normal directionand an area in which at least one of the conductive layers contacts arespective electrode formed on the substrate.

According to a further embodiment of the present invention, a processfor producing a semiconductor light-emitting device is provided. Theprocess includes the steps of forming an underlying layer on asubstrate, forming a masking layer having a window region on theunderlying layer, selectively growing a crystal grown layer through thewindow region, and forming a first conductive layer, an active layer,and a second conductive layer on a surface of the crystal grown layer,wherein the active layer includes a crystal surface with a surface arealarger than a projected area derived from projecting the crystal surfacetoward the substrate in a normal direction.

According to another embodiment of the present invention, a process forproducing a semiconductor light-emitting device is provided. The processincludes the steps of providing a first substrate including a firstsubstrate surface oriented along a first substrate surface plane,forming a crystal seed layer on the first substrate surface, forming amasking layer on the crystal seed layer, wherein the masking layerincludes an opening, forming a crystal layer by selective growth of thecrystal seed layer through the opening of the masking layer, wherein thecrystal layer includes a crystal layer surface oriented along a crystallayer plane that diagonally intersects the first substrate surfaceplane, forming each of a first conductive layer, an active layer, and asecond conductive layer along at least a portion of the crystal layersurface, embedding each of the first conductive layer, the active layerand the second conductive layer and the second conductive layer in aresin material layer formed on a second substrate, removing the secondsubstrate by laser abrasion, separating the crystal seed layer andmasking layer from a substrate region of the substrate, and forming anelectrode on at least a portion of the substrate region.

In an embodiment, the crystal seed layer and the masking layer areseparated by peeling off.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the Figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sectional view showing a structure of a semiconductorlight-emitting device.

FIG. 2 is a sectional view showing another structure of a semiconductorlight-emitting device.

FIGS. 3A and 3B are diagrams showing the step of forming a mask in theproduction of the semiconductor light-emitting device in Example 1 of anembodiment of the present invention, wherein FIG. 3A is a sectional viewand FIG. 3B is a perspective view.

FIGS. 4A and 4B are diagrams showing the step of forming a silicon-dopedGaN layer in the production of the semiconductor light-emitting devicein Example 1 of an embodiment of the present invention, wherein FIG. 4Ais a sectional view and FIG. 4B is a perspective view.

FIGS. 5A and 5B are diagrams showing the step of forming a window forcrystal growth in the production of the semiconductor light-emittingdevice in Example 1 of an embodiment of the present invention, whereinFIG. 5A is a sectional view and FIG. 5B is a perspective view.

FIGS. 6A and 6B are diagrams showing the step of forming an active layeretc. in the production of the semiconductor light-emitting device inExample 1 of an embodiment of the present invention, wherein FIG. 6A isa sectional view and FIG. 6B is a perspective view.

FIGS. 7A and 7B are diagrams showing the step of forming an electrode inthe production of the semiconductor light-emitting device in Example 1of an embodiment of the present invention, wherein FIG. 7A is asectional view and FIG. 7B is a perspective view.

FIGS. 8A and 8B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 1of an embodiment of the present invention, wherein FIG. 8A is asectional view and FIG. 8B is a perspective view.

FIG. 9 is a sectional view showing the structure of the semiconductorlight-emitting device in Example 1 of an embodiment of the presentinvention.

FIGS. 10A and 10B are diagrams showing the step of forming a mask in theproduction of the semiconductor light-emitting device in Example 2 of anembodiment of the present invention, wherein FIG. 10A is a sectionalview and FIG. 10B is a perspective view.

FIGS. 11A and 11B are diagrams showing the step of selective removal inthe production of the semiconductor light-emitting device in Example 2of an embodiment of the present invention, wherein FIG. 11A is asectional view and FIG. 11B is a perspective view.

FIGS. 12A and 12B are diagrams showing the step of forming a crystallayer in the production of the semiconductor light-emitting device inExample 2 of an embodiment of the present invention, wherein FIG. 12A isa sectional view and FIG. 12B is a perspective view.

FIGS. 13A and 13B are diagrams showing the step of forming an activelayer in the production of the semiconductor light-emitting device inExample 2 of an embodiment of the present invention, wherein FIG. 13A isa sectional view and FIG. 13B is a perspective view.

FIGS. 14A and 14B are diagrams showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example2 of an embodiment of the present invention, wherein FIG. 14A is asectional view and FIG. 14B is a perspective view.

FIGS. 15A and 15B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 2of an embodiment of the present invention, wherein FIG. 15A is asectional view and FIG. 15B is a perspective view.

FIG. 16 is a sectional view showing the semiconductor light-emittingdevice in Example 2 of an embodiment of the present invention.

FIGS. 17A and 17B are diagrams showing the step of separating devices ina modified way in the production of the semiconductor light-emittingdevice in Example 2 of an embodiment of the present invention, whereinFIG. 17A is a sectional view and FIG. 17B is a perspective view.

FIGS. 18A and 18B are diagrams showing the step of forming a mask in theproduction of the semiconductor light-emitting device in Example 3 of anembodiment of the present invention, wherein FIG. 18A is a sectionalview and FIG. 18B is a perspective view.

FIGS. 19A and 19B are diagrams showing the step of forming a crystallayer in the production of the semiconductor light-emitting device inExample 3 of an embodiment of the present invention, wherein FIG. 19A isa sectional view and FIG. 19B is a perspective view.

FIGS. 20A and 20B are diagrams showing the step of forming an activelayer in the production of the semiconductor light-emitting device inExample 3 of an embodiment of the present invention, wherein FIG. 20A isa sectional view and FIG. 20B is a perspective view.

FIGS. 21A and 21B are diagrams showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example3 of an embodiment of the present invention, wherein FIG. 21A is asectional view and FIG. 21B is a perspective view.

FIGS. 22A and 22B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 3of an embodiment of the present invention, wherein FIG. 22A is asectional view and FIG. 22B is a perspective view.

FIG. 23 is a sectional view showing the semiconductor light-emittingdevice in Example 3 of an embodiment of the present invention.

FIGS. 24A and 24B are diagrams showing the step of forming a mask in theproduction of the semiconductor light-emitting device in Example 4 of anembodiment of the present invention, wherein FIG. 24A is a sectionalview and FIG. 24B is a perspective view.

FIGS. 25A and 25B are diagrams showing the step of forming a crystallayer in the production of the semiconductor light-emitting device inExample 4 of an embodiment of the present invention, wherein FIG. 25A isa sectional view and FIG. 25B is a perspective view.

FIGS. 26A and 26B are diagrams showing the step of forming an activelayer in the production of the semiconductor light-emitting device inExample 4 of an embodiment of the present invention, wherein FIG. 26A isa sectional view and FIG. 26B is a perspective view.

FIGS. 27A and 27B are diagrams showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example4 of an embodiment of the present invention, wherein FIG. 27A is asectional view and FIG. 27B is a perspective view.

FIGS. 28A and 28B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 4of an embodiment of the present invention, wherein FIG. 28A is asectional view and FIG. 28B is a perspective view.

FIG. 29 is a sectional view showing the semiconductor light-emittingdevice in Example 4 of an embodiment of the present invention.

FIGS. 30A and 30B are diagrams showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example5 of an embodiment of the present invention, wherein FIG. 30A is asectional view and FIG. 30B is a perspective view.

FIGS. 31A and 31B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 5of an embodiment of the present invention, wherein FIG. 31A is asectional view and FIG. 31B is a perspective view.

FIG. 32 is a sectional view showing the semiconductor light-emittingdevice in Example 5 of an embodiment of the present invention.

FIGS. 33A and 33B are diagrams showing the step of forming a p-electrodein the production of the semiconductor light-emitting device in Example6 of an embodiment of the present invention, wherein FIG. 33A is asectional view and FIG. 33B is a perspective view.

FIGS. 34A and 34B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 6of an embodiment of the present invention, wherein FIG. 34A is asectional view and FIG. 34B is a perspective view.

FIGS. 35A and 35B are diagrams showing the step of forming ann-electrode in the production of the semiconductor light-emitting devicein Example 6 of an embodiment of the present invention, wherein FIG. 35Ais a sectional view and FIG. 35B is a perspective view.

FIGS. 36A, 36B and 36C are diagrams showing the step of forming ann-electrode in a modified way according to an embodiment of the presentinvention, wherein FIG. 36A is a schematic sectional view snowing thelaser abrasion step, FIG. 36B is a schematic sectional view showing theRIE step, and FIG. 36C is a schematic sectional view showing the step offorming an n-electrode.

FIG. 37 is a sectional view showing the semiconductor light-emittingdevice in Example 6 of an embodiment of the present invention.

FIG. 38 is a rear perspective view showing another structure of thesemiconductor light-emitting device in Example 6 of an embodiment of thepresent invention.

FIGS. 39A and 39B are diagrams showing the step of forming a transparentelectrode in the production of the modified semiconductor light-emittingdevice in Example 6 of an embodiment of the present invention, whereinFIG. 39A is a sectional view and FIG. 39B is a perspective view.

FIG. 40 is a sectional view showing the modified semiconductorlight-emitting device in Example 6 of an embodiment of the presentinvention.

FIG. 41 is a perspective view showing the step of forming a mask in theproduction of the semiconductor light-emitting device in Example 7 of anembodiment of the present invention.

FIG. 42 is a perspective view showing the step of forming an activelayer in the production of the semiconductor light-emitting device inExample 7 of an embodiment of the present invention.

FIG. 43 is a perspective view showing the step of forming an electrodein the production of the modified semiconductor light-emitting device inExample 7 of an embodiment of the present invention.

FIG. 44 is a sectional view showing the semiconductor light-emittingdevice in Example 7 of an embodiment of the present invention.

FIGS. 45A and 45B are diagrams showing the step of forming a mask in theproduction of the semiconductor light-emitting device in Example 8 of anembodiment of the present invention, wherein FIG. 45A is a sectionalview and FIG. 45B is a perspective view.

FIGS. 46A and 46B are diagrams showing the step of forming a crystallayer in the production of the semiconductor light-emitting device inExample 8 of an embodiment of the present invention, wherein FIG. 46A isa sectional view and FIG. 46B is a perspective view.

FIGS. 47A and 47B are diagrams showing the step of forming an activelayer in the production of the semiconductor light-emitting device inExample 8 of an embodiment of the present invention, wherein FIG. 47A isa sectional view and FIG. 47B is a perspective view.

FIGS. 48A and 48B are diagrams showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example8 of an embodiment of the present invention, wherein FIG. 48A is asectional view and FIG. 48B is a perspective view.

FIGS. 49A and 49B are diagrams showing the step of separating devices inthe production of the semiconductor light-emitting device in Example 8of an embodiment of the present invention, wherein FIG. 49A is asectional view and FIG. 49B is a perspective view.

FIG. 50 is a sectional view showing the semiconductor light-emittingdevice in Example 8 of an embodiment of the present invention.

FIGS. 51A and 51B are diagrams showing the step of forming an electrodein the production of the modified semiconductor light-emitting device inExample 8 of an embodiment of the present invention, wherein FIG. 51A isa sectional view and FIG. 51B is a perspective view.

FIG. 52 is a sectional view showing the modified semiconductorlight-emitting device in Example 8 of an embodiment of the presentinvention.

FIGS. 53A and 53B are diagrams showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example9 of an embodiment of the present invention, wherein FIG. 53A is asectional view and FIG. 53B is a perspective view.

FIG. 54 is a partial perspective view showing an apparatus that utilizesthe semiconductor light-emitting device in Example 10 of an embodimentof the present invention.

FIG. 55 is a sectional view showing the structure of the semiconductorlight-emitting device in Example 11 of an embodiment of the presentinvention.

FIG. 56 is a sectional view illustrating the area W1 of the windowregion of the semiconductor light-emitting device in Example 11 of anembodiment of the present invention.

FIG. 57 is a sectional view illustrating the projected area W2 of thecrystal grown layer of the semiconductor light-emitting device inExample 11 of an embodiment of the present invention.

FIG. 58 is a perspective view showing the structure of the semiconductorlight-emitting device in Example 12 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a stripe pattern.

FIG. 59 is a perspective view showing the structure of the semiconductorlight-emitting device in Example 13 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of elongated quadrangular prismoids.

FIG. 60 is a perspective view showing the structure of the semiconductorlight-emitting device in Example 14 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of quadrangular prismoids.

FIG. 61 is a perspective view showing the structure of the semiconductorlight-emitting device Example 15 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of hexagonal pyramids.

FIG. 62 is a perspective view showing the structure of the semiconductorlight-emitting device Example 16 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of hexagonal prismoids.

FIG. 63 is a perspective view showing the step of forming an underlyinglayer for growth in the production of the semiconductor light-emittingdevice in Example 17 of an embodiment of the present invention.

FIG. 64 is a perspective view showing the step of forming window regionsin the production of the semiconductor light-emitting device in Example17 of an embodiment of the present invention.

FIG. 65 is a perspective view showing the step of forming a crystalgrown layer in the production of the semiconductor light-emitting devicein Example 17 of an embodiment of the present invention.

FIG. 66 is a perspective view showing the step of forming a layer of asecond conductivity type in the production of the semiconductorlight-emitting device in Example 17 of an embodiment of the presentinvention.

FIG. 67 is a perspective view showing the step of forming a contactregion in the production of the semiconductor light-emitting device inExample 17 of an embodiment of the present invention.

FIG. 68 is a perspective view showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example17 of an embodiment of the present invention.

FIG. 69 is a sectional view showing the semiconductor light-emittingdevice in Example 18 of an embodiment of the present invention.

FIG. 70 is a sectional view showing the structure of the semiconductorlight-emitting device in Example 19 of an embodiment of the presentinvention.

FIG. 71 is a sectional view showing a portion of the semiconductorlight-emitting device in Example 19 of an embodiment of the presentinvention.

FIG. 72 is a perspective view showing the model of crystal grown layerthat is used as the basis for calculations in production of thesemiconductor light-emitting device in the Examples of an embodiment ofthe present invention.

FIG. 73 is a schematic diagram showing the model which is used forcalculations of angle dependence in production of the semiconductorlight-emitting device in Examples of an embodiment of the presentinvention.

FIG. 74 is a line graph showing the angle dependence on the lightemergence efficiency which is obtained from the above-mentionedcalculations in accordance with an embodiment of the present invention.

FIG. 75 is a schematic diagram showing the model which is used forcalculations of height dependence in production of the semiconductorlight-emitting device in Examples of an embodiment of the presentinvention.

FIG. 76 is a line graph showing the height dependence on the lightemergence efficiency which is obtained from the above-mentionedcalculations in accordance with an embodiment of the present invention.

FIG. 77 is a perspective view showing the structure of the semiconductorlight-emitting device in Example 20 of the present invention that ischaracterized by the crystal grown layer which is formed in a stripepattern in accordance with an embodiment of the present invention.

FIG. 78 is a perspective view showing the structure of the semiconductorlight-emitting device in Example 21 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of elongated quadrangular prismoids.

FIG. 79 is a perspective view showing the structure of the semiconductorlight-emitting device in Example 22 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of quadrangular prismoids.

FIG. 80 is a perspective view showing the structure of the semiconductorlight-emitting device Example 23 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of hexagonal pyramids.

FIG. 81 is a perspective view showing the structure of the semiconductorlight-emitting device Example 24 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a pattern of hexagonal prismoids.

FIG. 82 is a perspective view showing the structure of the semiconductorlight-emitting device Example 25 of an embodiment of the presentinvention that is characterized by the crystal grown layer which isformed in a mixed pattern of hexagonal pyramids and quadrangularprismoids.

FIG. 83 is a perspective view showing the step of forming an underlyinglayer for growth in the production of the semiconductor light-emittingdevice in Example 25 of an embodiment of the present invention.

FIG. 84 is a perspective view showing the step of forming window regionsin the production of the semiconductor light-emitting device in Example25 of an embodiment of the present invention.

FIG. 85 is a perspective view showing the step of forming a crystalgrown layer in the production of the semiconductor light-emitting devicein Example 25 of an embodiment of the present invention.

FIG. 86 is a perspective view showing the step of forming a layer of asecond conductivity type in the production of the semiconductorlight-emitting device in Example 25 of an embodiment of the presentinvention.

FIG. 87 is a perspective view showing the step of forming a contactregion in the production of the semiconductor light-emitting device inExample 25 of an embodiment of the present invention.

FIG. 88 is a perspective view showing the step of forming an electrodein the production of the semiconductor light-emitting device in Example25 of an embodiment of the present invention.

FIG. 89 is a sectional view showing the semiconductor light-emittingdevice in Example 26 of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A semiconductor light-emitting device according to an embodiment of thepresent invention includes a substrate and a crystal layer formedthereon, the crystal layer having a slant crystal plane slanting to(i.e., diagonally intersecting) the principal plane of the substrate,and further includes a layer of a first conductivity type, an activelayer, and a layer of a second conductivity type which are formedparallel to the slant crystal plane on the crystal layer.

The substrate used in an embodiment of the present invention is notspecifically restricted so long as it forms a crystal layer having aslant crystal plane slanting to the principal plane of the substrate.Various substrates are available including, for example, sapphire(Al2O3, having A-plane, R-plane, or C-plane), SiC (including 6H, 4H, and3C), GaN, Si, ZnS, ZnO, AlN, LiMgO, GaAs, MgAl2O4, and InAlGaN. Of theabove-described substrates, hexagonal or cubic crystal based substratesare preferred, with the hexagonal substrates being most preferred. Asapphire substrate whose principal plane is the C-plane can be used. Ingeneral, the C-plane is a plane on which a gallium nitride (GaN) basedcompound for a semiconductor is usually grown, and the C-plane as theprincipal plane of the substrate may have a plane orientation which isinclined at an angle of 5 or 6 degrees.

In an embodiment, the substrate itself is not a constituent of thelight-emitting device and is used merely to hold device parts and isremoved before the device is completed.

In an embodiment, the crystal layer formed on the substrate has a slantcrystal plane slanting to the principal plane of the substrate. Thiscrystal layer is not specifically restricted so long as it permits thelight-generating region (mentioned later) to be formed thereon, whichconsists of a layer of a first conductivity type, an active layer, and alayer of a second conductivity type, and is parallel to the slantcrystal plane slanting to the principal plane of the substrate. Amaterial of a wurtzite crystal structure is desirable for the crystallayer. However, it should be appreciated that a variety of suitablecrystal structures can be utilized.

The crystal layer can be formed of a variety of different and suitablematerials. In an embodiment, the crystal layer may be formed from agroup III based compound semiconductor, a BeMgZnCdS based compoundsemiconductor, a BeMgZnCdO based compound semiconductor, a galliumnitride (GaN) based compound semiconductor, an aluminum nitride (AlN)based compound semiconductor, an indium nitride (InN) based compoundsemiconductor, an indium gallium nitride (InGaN) based compoundsemiconductor, an aluminum gallium nitride (AlGaN) based compoundsemiconductor, the like and combinations thereof. In an embodiment,Nitride semiconductors such as a gallium nitride based compoundsemiconductor are preferred.

It should be noted that in the present invention, InGaN, AlGaN, GaN, andthe like do not necessarily imply nitride semiconductors of ternary orbinary mixed crystals alone. InGaN, for example, may contain a traceamount of Al and other impurities which do not affect the function ofInGaN. Such compound semiconductors are within the scope of the presentinvention.

The crystal layer can be grown by chemical vapor deposition of variouskinds, such as metal organic chemical vapor deposition (MOCVD)including, for example, metal organic vapor phase epitaxy (MOVPE),molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), andthe like. In an embodiment, MOCVD is preferred because it rapidly yieldsa crystal layer with desirable crystal properties. The MOCVD methodcommonly employs alkyl metal compounds, such as TMG (trimethylgallium)or TEG (triethylgallium) as a Ga source, TMA (trimethylaluminum) or TEA(triethylaluminum) as an Al source, and TMI (trimethylindium) or TEI(triethylindium) as an In source. It also employs ammonia gas orhydrazine gas as a nitrogen source, and other gases as an impuritysource, for example, silane gas for Si, germane gas for Ge, Cp2Mg(cyclopentadienylmagnesium) for Mg, and DEZ (diethylzinc) for Zn. Ingeneral, MOCVD is carried out by feeding the gases to the surface of thesubstrate which is heated at about 600° C. or above, so that the gasesdecompose to give an InAlGaN based compound semiconductor by epitaxialgrowth.

It is desirable, in an embodiment, that the crystal layer be formedafter an underlying layer for growth has been formed on the substrate.In an embodiment, the underlying layer for growth may be a galliumnitride layer, an aluminum nitride layer, or the like. It may also be acombination of a low-temperature buffer layer and a high-temperaturebuffer layer, or a combination of a buffer layer and a crystal seedlayer (functioning as a crystal seed). As in the crystal layer, theunderlying layer for growth can also be formed by chemical vapordeposition such as metal organic chemical vapor deposition (MOCVD),molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), andthe like. Growing the crystal layer from the low-temperature bufferlayer causes a problem that polycrystals are likely to precipitate onthe mask. This problem is overcome by forming a crystal seed layer andthen growing thereon a plane differing from the substrate. Thus, it ispossible to grow crystals having desirable crystal properties. In thecase of selective growth for crystal growing, it is necessary to growcrystals from the buffer layer if there exists no crystal seed layer.Selective growth from the buffer layer causes crystals to grow from thepart where the crystal growth is not required. Consequently, the crystalseed layer permits crystals to grow selectively in the region wherecrystal growth is necessary. The buffer layer is intended to relievelattice mismatch between the substrate and the nitride semiconductor.Therefore, there may be an instance where the buffer layer is not formedif the substrate has a lattice constant close to that of the nitridesemiconductor. For example, there may be an instance where an AlN bufferlayer is formed on SiC without lowering temperature or an AlN or GaNbuffer layer is formed on a Si substrate without lowering temperature.Thus, it is also possible to form GaN of good quality. The structurewithout any buffer layer is acceptable if the substrate is GaN or asuitable material.

According to an embodiment of the present invention, selective growthcan be used to form the slant crystal plane slanting to the principalplane of the substrate. The slant crystal plane slanting to theprincipal plane of the substrate depends on the principal plane of thesubstrate used. It is selected from such crystal planes as the

-   -   (1–100) plane [M-plane], the (1–101) plane [S-plane], the        (11–20) plane [A-plane], the (1–102) plane [R-plane], the        (11–23) plane [N-plane], the (11–22) plane, the like and        combinations thereof when the principal plane of the substrate        is the (0001) plane [C-plane] of a wurtzite structure.

It is noted that the plane terminology (e.g., S-plane, C-plane or thelike) as used herein denotes crystal planes in accordance with Millerindices of a hexagonal crystal system. Where appropriate, throughout thespecification, these planes are intended to include more than one planein the hexagonal crystal system. For example, the S-plane is listedabove as corresponding to the (1–101) plane, but it should be understoodthat, where appropriate, the S-plane is intended to include one or moreof the planes relating to the family of planes making up a crystalstructure having the S-plane. For example, if the crystal structurebeing described is a hexagonal pyramid having the S-plane, planescorresponding to each side face of the hexagonal pyramid would beincluded in the family of planes denoted by the S-plane. For example, inaddition to the (1–101) plane, a hexagonal pyramid has side facescorresponding to the (10–11), (01–11), (-1101) and (0–111) planes.

In an embodiment, the S-plane and the (11–22) plane are preferred.Naturally, equivalent crystal planes may also be used, for example,planes having a plane orientation inclined at an angle of about 5 toabout 6 degrees to the S-plane or the (11–22) plane. In particular, theS-plane is a stable plane which is obtained when selective growth iscarried out on the C+-plane. The S-plane can be obtained comparativelyeasily, and it is expressed as a (1–101) plane in accordance with Millerindices of a hexagonal crystal system. Just as the C-plane includes theC+-plane and the C−-plane, the S-plane includes the S+-plane and theS−-plane. In this specification, the S+-plane is grown on the C+-planeGaN and it is referred to as the S-plane unless otherwise stated.Additionally, of the S-planes, the S+-plane is stable.

The index of the C+-plane is (0001). In the case where the crystal layeris formed from a gallium nitride based compound semiconductor (asmentioned above), the number of bonds from Ga to N is 2 or 3 on theS-plane. This number is second to that on the C-plane. Since theC−-plane cannot be obtained on the C+-plane in practice, the number ofbonds on the S-plane is the largest. For example, when a nitride isgrown on a sapphire substrate having the C-plane as the principal plane,the nitride of wurtzite structure has a surface of C+-plane. However, itis possible to form the S-plane if selective growth is employed. On theplane parallel to the C-plane, the bond of N (which easily releasesitself) combines with one bond of Ga, whereas on the slant S-plane, itcombines with at least one bond. This causes the effective V/III ratioto increase, thereby improving the crystal properties of the laminatestructure. In addition, growth in the direction different from theorientation of the substrate bends dislocations extending from thesubstrate, thereby favorably decreasing defects.

In a semiconductor light-emitting device according to an embodiment ofthe present invention, the crystal layer has a slant crystal planeslanting to the principal plane of the substrate. The crystal layer maybe formed such that the S-plane (or any other plane substantiallyequivalent thereto) constitutes the side faces of an approximatelyhexagonal pyramid, or the S-plane (or any other plane substantiallyequivalent thereto) constitutes the side faces of an approximatelyhexagonal prismoid and the C-plane (or any other plane substantiallyequivalent thereto) constitutes the top plane of the approximatelyhexagonal prismoid. The approximately hexagonal pyramid andapproximately hexagonal prismoid do not necessarily need to be exactlyhexagonal. They may include those which have one or more missing faces.In a preferred embodiment, the slant crystal plane is hexagonal and isarranged approximately symmetrical. The term “approximatelysymmetrical,” as used herein, embraces completely symmetrical andslightly asymmetrical. The edge between the crystal planes of thecrystal layer does not necessarily need to be straight. Also, theapproximately hexagonal pyramid or approximately hexagonal prismoid maybe in an elongated shape.

In actuality, selective growth is accomplished in an embodiment by usinga selectively removed part of the underlying layer for growth or byusing a selectively made opening in the masking layer on the underlyinglayer for growth or in the masking layer which is formed before theunderlying layer for growth has been formed. For example, when theunderlying layer for growth consists of a buffer layer and a crystalseed layer, the crystal seed layer on the buffer layer is divided intoscattered small regions, each about 10 μm in diameter. Crystals aregrown from these small regions such that the crystal layer having theS-plane is formed. For example, the finely divided crystal seed layersmay be arranged apart from one another, thereby allowing finishedlight-emitting devices to be separated. Individual small regions maytake on any shape such as a stripe, a lattice, a circle, a square, ahexagon, a triangle, a rectangle, a rhombus, the like and combinationsthereof. Selective growth may also be accomplished by forming a maskinglayer on the underlying layer for growth and selectively formingopenings (i.e., window regions) in the masking layer. In an embodiment,the masking layer may be a silicon oxide layer, a silicon nitride layer,or the like. The approximately hexagonal pyramids or prismoids in anelongated shape (as mentioned above) may be formed if the window regionin the masking layer or the crystal seed layer is formed in an elongatedshape.

In an embodiment, if the window region in the masking layer forselective growth is a circle of about 10 μm in diameter (or a hexagonwhose one side coincides with the (1–100) direction or (11–20)direction), it is possible to easily form a selectively grown regionwhich is about twice as large as the window region. Also, the S-plane ina direction different from the substrate produces the effect of bendingor isolating dislocations. This contributes to reduction in the densityof dislocations.

Observation by cathode luminescence on the grown hexagonal prismoidindicates that the S-plane has desirable crystal properties and issuperior to the C+-plane in light emission efficiency. Growing the InGaNactive layer at about 700° C. to about 800° C. makes ammonia decomposeslowly and hence, requires more nitrogen species. Observations with anAFM revealed that the surface has regular steps suitable for InGaNuptake. It was also found that the Mg-doped layer, whose grown surfaceobserved by AFM is usually in poor state, improves owing to the S-planeand that the doping condition is considerably different. Observation bymicroscopic photoluminescence mapping (which has a resolving power ofabout 0.5 μm to about 1 μm) revealed that the S-plane formed byselective growth is uniform. The S-plane formed on the C+-plane by theordinary process has irregularities at a pitch of about 1 μm. Also,observation with an SEM revealed that the side face is smoother than theC+-plane.

If selective growth is carried out, using a mask, such that crystalsgrow only over the opening of the mask, crystals do not grow in thelateral direction. Thus, it is possible to employ microchannel epitaxyto make crystals to grow in the lateral direction, extending beyond thewindow region. It is known that growing in the lateral direction bymicrochannel epitaxy readily avoids threading dislocations and hence,reduces dislocations. Thus, growing in the lateral direction gives anenlarged light-generating region and contributes to uniform current flowand reduced current density.

A semiconductor light-emitting device according to an embodiment of thepresent invention includes a substrate and a crystal layer formedthereon, the crystal layer having a slant crystal plane slanting to theprincipal plane of the substrate, and further includes a layer of afirst conductivity type, an active layer, and a layer of a secondconductivity type which are formed parallel to the slant crystal planeon the crystal layer. The layer of a first conductivity type is acladding layer of p-type or n-type, and the layer of a secondconductivity type is a cladding layer of an opposite type. For example,if the crystal layer constituting the S-plane is formed from asilicon-doped gallium nitride based compound semiconductor layer, ann-type cladding layer is formed from a silicon-doped gallium nitridecompound semiconductor. On this cladding layer, an active layer of InGaNis formed. On this active layer, a p-type cladding layer ofmagnesium-doped gallium nitride based compound semiconductor is formed.Thus, the desired double heterojunction structure is obtained. Anotherpossible structure is such that the active layer of InGaN is heldbetween two AlGaN layers. The active layer may be of a single bulk layerstructure. Alternatively, it may be of single quantum well (SQW)structure, double quantum well (DQW) structure, or multiple quantum well(MQW) structure. The quantum well structure may use a barrier layer forseparation of quantum wells, if necessary. The light-emitting devicehaving an active layer of InGaN is easy to produce and has desirablelight emission characteristics. Moreover, the InGaN layer readilycrystallizes and has desirable crystal properties on the S-plane fromwhich nitrogen atoms hardly release themselves, thereby increasing thelight emission efficiency.

Additionally, a nitride compound semiconductor tends to become n-typedue to nitrogen holes which occur in crystal even though it is notdoped. However, it can be deliberately made n-type, having a desiredcarrier density, if it is doped with an ordinary donor impurity (such asSi, Ge, and Se) during crystal growth. Also, a nitride semiconductor canbe made p-type by doping with an acceptor impurity (such as Mg, Zn, C,Be, Ca, and Ba). In order to obtain a p-layer with a high carrierdensity, it is desirable to subject it to annealing at about 400° C. ormore in an inert gas atmosphere (such as nitrogen and argon) afterdoping with an acceptor impurity. Activation by irradiation withelectron beams, microwaves, or light is also available.

In an embodiment, the layer of a first conductivity type, the activelayer, and the layer of a second conductivity type are parallel to theslant crystal plane slanting to the principal plane of the substrate.They are easily formed by crystal growth following the formation of theslant crystal plane. When the crystal layer forms approximatelyhexagonal pyramids or prismoids and the slant crystal plane is theS-plane, the light-generating region (consisting of the layer of a firstconductivity type, the active layer, and the layer of a secondconductivity) may be formed entirely or partly on the S-plane.

With an approximately hexagonal prismoid, the layer of a firstconductivity type, the active layer, and the layer of a secondconductivity type may also be formed on its top face, parallel to theprincipal plane of the substrate. One advantage of light emission by theslant S-plane is that light emerges from the semiconductor withoutmultiple reflection owing to the slant planes. In contrast, withparallel planes, light attenuates due to multiple reflection.) The layerof a first conductivity type (or the cladding layer) may have the sameconductivity type if it is made from the same material as used for thecrystal layer constituting the S-plane. It is also possible to form bycontrolling the density continuously after the crystal layerconstituting the S-plane has been formed. In an embodiment, thestructure may be such that part of the crystal layer constituting theS-plane functions as the layer of a first conductivity type. Also, lightemergence is improved when the plane is not perpendicular to thesubstrate.

A semiconductor light-emitting device according to an embodiment of thepresent invention offers improved light emission efficiency by virtue ofdesirable crystal properties possessed by the slant crystal plane. Thelight emission efficiency can be increased if current is injected onlyinto the S-plane having desirable crystal properties owing to itsadvantageous uptake for In. The active layer, substantially parallel tothe S-plane, may have an area larger than that obtained by projectingthe active layer to the principal plane of the substrate or theunderlying layer for growth. The active layer with a large areaincreases the device's emitting surface, thereby leading to a reductionin current density. Moreover, the active layer, with a large area,decreases brightness saturation and hence, increases light emissionefficiency.

In an embodiment, with the crystal layer in the form of hexagonalpyramid, the S-plane is poor in step state particularly in the vicinityof the apex and the light emission efficiency is low at the apex. Thereason for this is that the hexagonal pyramid is constructed such thateach of its sides consists of four sections extending from its centertoward the apex, left edge, right edge, and base, and the sectionextending toward the apex is very wavy and anomalous growth readilyoccurs in the vicinity of the apex. In contrast, in the two sectionsextending toward both edges, steps are nearly straight and dense and ina very desirable grown state. In the section extending toward the base,steps are slightly wavy but crystal growth is not so anomalous as in thesection extending toward the apex. Thus, in the semiconductorlight-emitting device according to an embodiment of the presentinvention, it is possible to control current injection into the activelayer such that current density is lower in the vicinity of the apexthan in the surrounding areas. The structure to realize the low currentdensity in the vicinity of the apex is such that the electrode is formedat the side of the slope but is not formed at the apex or is such thatthe current block region is formed before the electrode is formed at theapex.

In an embodiment, electrodes are formed on the crystal layer and thelayer of a second conductivity type, respectively. For reduced contactresistance, the electrode may be formed on a previously formed contactlayer. These electrodes may be formed by vapor deposition. Accuratevapor deposition is necessary to avoid short-circuiting, which occurs asthe result of the p-electrode and n-electrode coming into contact withthe crystal layer and the crystal seed layer formed under the mask.

A semiconductor light-emitting device according to an embodiment of thepresent invention includes a substrate and a crystal layer formedthereon, the crystal layer having the slant S-plane (or a planesubstantially equivalent thereto) slanting to the principal plane of thesubstrate and further includes a layer of a first conductivity type, anactive layer, and a layer of a second conductivity type parallel to theS-plane or a plane substantially equivalent thereto which are formed onthe crystal layer. The substrate used herein is not specificallyrestricted so long as it forms a crystal layer having the S-plane or aplane equivalent thereto. It may be the same type of substrate used forthe semiconductor light-emitting device mentioned in the previousembodiment.

In an embodiment, the crystal layer formed on the substrate has theS-plane (or a plane substantially equivalent thereto) slanting to theprincipal plane of the substrate. This crystal layer may be formed fromany material which gives the light-generating region consisting of thelayer of a first conductivity type, the active layer, and the layer of asecond conductivity type parallel to the S-plane or a planesubstantially equivalent thereto. The same type of material mentioned inprevious embodiments may be used. The method for growing the crystallayer and the underlying layer for growth for the crystal layer may alsobe the same as those mentioned in the previously described embodiments.Also, the plane substantially equivalent to the S-plane has a planeorientation inclined toward the S-plane at an angle of about 5 to about6 degrees.

According to an embodiment of the present invention, it is possible touse selective growth to form the S-plane or a plane substantiallyequivalent thereto. The S-plane is a stable plane which is obtained byselective growth on the C+-plane and can be obtained comparativelyeasily with an index of (1–101) in the hexagonal crystal system. Just asthe C-plane includes the C⁺-plane and the C⁻-plane, so the S-planeincludes the S⁺-plane and the S⁻-plane. In an embodiment, the S⁺-planeis grown on the C⁺-plane GaN and it is referred to as the S-plane unlessotherwise stated.

According to an embodiment of the present invention, a semiconductorlight-emitting device is constructed such that the crystal layer has atleast the S-plane or a plane substantially equivalent thereto. Thecrystal layer may be such that the S-plane (or any other planesubstantially equivalent thereto) constitutes the side faces of anapproximately hexagonal pyramid, or the S-plane (or any other planesubstantially equivalent thereto) constitutes the side faces of anapproximately hexagonal prismoid and the C-plane (or any other planesubstantially equivalent thereto) constitutes the top of theapproximately hexagonal prismoid. The approximately hexagonal pyramid orapproximately hexagonal prismoid does not necessarily need to be exactlyhexagonal. It may include those which have one or more missing faces orhave edges which are not straight. The approximately hexagonal pyramidor approximately hexagonal prismoid may be in an elongated shape. Themethod for selective growth is the same as that used in the previouslydescribed embodiments.

A semiconductor light-emitting device according to an embodiment of thepresent invention has the layer of a first conductivity type, the activelayer, and the layer of a second conductivity type parallel to theS-plane or a plane substantially equivalent thereto, which are formed onthe crystal layer. The layer of a first conductivity type, the activelayer, and the layer of a second conductivity type are similar to thoseexplained in the previous embodiments.

In an embodiment, the layer of a first conductivity type, the activelayer, and the layer of a second conductivity type are parallel to theS-plane or a plane substantially equivalent thereto. They are easilyformed by continuous crystal growth in the place where the S-plane hasbeen formed. When the crystal layer forms approximately hexagonalpyramids or prismoids and the slant plane is the S-plane, thelight-generating region (consisting of the layer of a first conductivitytype, the active layer, and the layer of a second conductivity) may beformed entirely or partly on the S-plane. With an approximatelyhexagonal prismoid, the layer of a first conductivity type, the activelayer, and the layer of a second conductivity may also be formed on itstop face parallel to the principal plane of the substrate. One advantageof light emission utilizing the slant S-plane is that light emerges fromthe semiconductor without multiple reflection owing to the slant planes.With parallel planes, light attenuates due to multiple reflection. Thelayer of a first conductivity type (or the cladding layer) may have thesame conductivity type if it is made from the same material as used forthe crystal layer constituting the S-plane. It is also possible to formby controlling the density continuously after the crystal layerconstituting the S-plane has been formed. In an embodiment, thestructure may be such that part of the crystal layer constituting theS-plane functions as the layer of a first conductivity type.

A semiconductor light-emitting device according to an embodiment of thepresent invention offers improved light emission efficiency by virtue ofdesirable crystal properties possessed by the slant S-plane. The lightemission efficiency can be increased if current is injected only intothe S-plane having desirable crystal properties owing to its beneficialuptake for In. The active layer substantially parallel to the S-planemay have an area larger than that obtained by projecting the activelayer to the principal plane of the substrate or the underlying layerfor growth. The active layer, with a large area, increases the device'semitting surface, thereby leading to a reduction in current density.Moreover, the active layer, with a large area, decreases brightnesssaturation and hence, increases light emission efficiency.

In an embodiment, with the crystal layer in the form of hexagonalpyramid, the S-plane is poor in step state particularly in the vicinityof the apex and the light emission efficiency is low at the apex. Thereason for this is that the hexagonal pyramid is constructed such thateach of its sides consists of four sections extending from its centertoward the apex, left edge, right edge, and base, and the sectionextending toward the apex is very wavy and anomalous growth readilyoccurs in the vicinity of the apex. In contrast, in the two sectionsextending toward both edges, steps are nearly straight and dense and ina very desirable grown state. In the section extending toward the base,steps are slightly wavy but crystal growth is not so anomalous as in thesection extending toward the apex. Thus, in the semiconductorlight-emitting device according to an embodiment of the presentinvention, it is possible to control current injection into the activelayer such that current density is lower in the vicinity of the apexthan in the surrounding areas. The structure to realize the low currentdensity in the vicinity of the apex is such that the electrode is formedat the side of the slope but is not formed at the apex or is such thatthe current block region is formed before the electrode is formed at theapex.

In an embodiment, electrodes are formed on the crystal layer and thelayer of a second conductivity, respectively. For reduced contactresistance, the electrode may be formed on a previously formed contactlayer. These electrodes may be formed by vapor deposition. Accuratevapor deposition is necessary to avoid short-circuiting, which occurs asthe result of the p-electrode and n-electrode coming into contact withthe crystal layer and the crystal seed layer formed under the mask.

A semiconductor light-emitting device according to an embodiment of thepresent invention includes a crystal grown layer having a slant crystalplane which is formed by selective growth and slants to the principalplane of the substrate, an active layer which is formed on the crystalgrown layer and emits light upon injection of current in a prescribedamount, and a reflecting plane or a reflecting region which is formedapproximately parallel to the slant crystal plane and reflects part oflight emerging from the active layer. The same concepts used in previousembodiments will be applicable to the substrate and crystal layer, theselective growth method of forming the crystal layer, and the basicconstitution of the layer of a first conductivity type, the activelayer, and the layer of a second conductivity type.

The reflecting plane or reflecting region in the semiconductorlight-emitting device according to an embodiment of the presentinvention is not specifically restricted in its structure so long as itreflects substantially all light generated by the active layer or it iscapable of effective reflection despite slight light transmission. Thisreflecting plane exists (at least partly) approximately parallel to theslant crystal plane. “Approximately parallel to the slant crystal plane”implies that the reflecting plane is either substantially parallel orslightly inclined. The reflecting plane may be a single plane or mayconsist of two or more planes parallel to the slant crystal planecapable of reflecting light generated by the active layer. Thereflecting planes may be constructed such that they overlap in thenormal direction of the slant crystal plane.

In a semiconductor light-emitting device according to an embodiment ofthe present invention, the crystal plane itself may function as thereflecting plane. The crystal plane functioning as the reflecting planereduces scattering and permits light to emerge efficiently. Moreover,when the crystal plane functions as the reflecting plane, it may beconstructed such that a metal film, as an electrode, can be formed aftereach semiconductor layer (such as the active layer) has been formed.Thus, the electrode constitutes a reflecting film. When the electrodeformed on the active layer is used as the reflecting film, if the activelayer is formed such that it is laminated on the slant crystal layer,the electrode can also be formed by itself in conformity with the shapeof the crystal grown layer, and fabrication such as etching isunnecessary for the formation of the reflecting film.

In an embodiment, the reflecting plane, parallel to the above-mentionedslant crystal plane, for example, may be constructed of at least tworeflecting planes facing each other at an angle smaller than 180°. Thesetwo or more reflecting planes facing each other at an angle smaller than180° may be two or more planes facing directly opposite to each other orplanes facing each other at other angles with a reflecting plane or acrystal plane interposed between them. For example, in the case of adevice in which the crystal grown layer of hexagonal pyramid structurehaving the S-plane as the side face is formed, they face each other atan angle of about 60° at the apex of the hexagonal pyramid.

In an embodiment, electrodes are formed on the crystal grown layer orthe first conductive layer and on the layer of a second conductivitytype, respectively. For reduced contact resistance, the electrode may beformed on a previously formed contact layer. These electrodes may beformed by vapor deposition. Accurate vapor deposition is necessary toavoid short-circuiting, which occurs as the result of the p-electrodeand n-electrode coming into contact with the crystal layer and thecrystal seed layer formed under the mask. If the fundamental structurein the present invention is to be applied to a light-emitting diode, theelectrodes may be formed on the first and second conductive layers,respectively. Either structure permits light to emerge from the front orreverse side, as desired. In other words, either structure permits lightto emerge from the reverse side if a transparent substrate is used oreither structure permits light to emerge from the front side if atransparent electrode is used.

One feature of a semiconductor light-emitting device according to anembodiment of the present invention is that the emerging light is partlyreflected by the reflecting plane which is parallel to the slant crystalplane formed by selective growth. Reflection improves the lightemergence efficiency, thereby causing the semiconductor light-emittingdevice to improve in brightness. Since the slant crystal plane as thebase of the reflecting plane can be easily formed by selective growth,the reflecting plane can be obtained by self-forming without additionalsteps, such as etching.

Another feature of a semiconductor light-emitting device according to anembodiment of the present invention is that the active layer has a largearea if it is formed by selective growth on a plane slant to thesubstrate for growth. When the device size is limited, the currentinjection density per unit area can be reduced for the same brightnesswhen the active layer in the device has a larger effective area.Therefore, the device with a larger effective area has improvedreliability for the same brightness and increased brightness for thesame load on the active layer. In particular, if the difference betweenthe total area of the active area and the area which the selectivelygrown region occupies in the substrate for growth is larger than thearea necessary for contact with at least one electrode, then thatportion of the active layer which is limited by the contact region iscompensated. Consequently, owing to the active layer formed on the slantcrystal plane, a semiconductor light-emitting device according to anembodiment of the present invention is less likely to experience asituation of current concentration even though its size is greatlyreduced.

A semiconductor light-emitting device according to an embodiment of thepresent invention includes a substrate, a first grown layer of a firstconductivity type formed on the substrate, a masking layer formed on thefirst grown layer, and a second grown layer of a first conductivity typewhich is formed by selective growth through an opening formed in themasking layer, and which further comprises a cladding layer of a firstconductivity type parallel to the crystal plane of the second grownlayer, an active layer, and a cladding layer of a second conductivitytype, part or all of which cover the masking layer surrounding theopening. The substrate used in this embodiment is not specificallyrestricted so long as it can form the crystal layer which has a slantcrystal plane slating to the principal plane of the substrate. It may bethe same type used for the previous embodiments.

In an embodiment, the substrate is formed the grown layer which consistsof a first grown layer (which is arranged under the masking layer) and asecond grown layer which is formed and grown from the opening in themasking layer. These first and second grown layers are of a firstconductivity type, but they are not specifically restricted so long asthey permit the light-generating region (which consists of a layer of afirst conductivity type, an active layer, and a layer of a secondconductivity type) to be formed on the plane parallel to the crystalplane of the second grown layer. The first and second grown layers maybe formed from a compound semiconductor, preferably that of a wurtzitestructure.

In an embodiment, the grown layer may be formed from a group III basedcompound semiconductor, a BeMgZnCdS based compound semiconductor, aBeMgZnCdO based compound semiconductor, or the like. It may be formedalso from a gallium nitride (GaN) based compound semiconductor, analuminum nitride (AlN) based compound semiconductor, an indium nitride(InN) based compound semiconductor, an indium gallium nitride (InGaN)based compound semiconductor, an aluminum gallium nitride (AlGaN) basedcompound semiconductor, the like or combinations thereof. Nitridesemiconductors such as a gallium nitride based compound semiconductorare preferred.

It should be noted that in the present invention, InGaN, AlGaN, GaN, andthe like do not necessarily imply nitride semiconductors of ternary orbinary mixed crystals alone. InGaN, for example, may contain a traceamount of Al and other impurities which do not affect the function ofInGaN. Such compound semiconductors are within the scope of the presentinvention. In this specification, “nitride” means a compound composed ofany of B, Al, Ga, In, and Ta as group III elements and mainly N as groupV elements. However, “nitride” in this specification also includes thosewhich have their bandgap reduced by incorporation with a trace amount ofAs and P.

In an embodiment, the grown layer can be formed by chemical vapordeposition of various kinds, such as metal-organic chemical vapordeposition (MOCVD) including, for example, metal organic vapor phaseepitaxy (MOVPE), molecular beam epitaxy (MBE), hydride vapor phaseepitaxy (HVPE), and the like. In an embodiment, MOCVD is preferredbecause it rapidly yields a grown layer with advantageous crystalproperties. The MOCVD method commonly employs alkyl metal compounds,such as TMG (trimethylgallium) or TEG (triethylgallium) as a Ga source,TMA (trimethylaluminum) or TEA (triethylaluminum) as an Al source, andTMI (trimethylindium) or TEI (triethylindium) as an In source. It alsoemploys ammonia gas or hydrazine gas as a nitrogen source and othergases as an impurity source, for example, silane gas for Si, germane gasfor Ge, Cp2Mg (cyclopentadienylmagnesium) for Mg, and DEZ (diethylzinc)for Zn. Usually, MOCVD is carried out by feeding the gases to thesurface of the substrate which is heated at about 600° C. or above, sothat the gases decompose to give an InAlGaN based compound semiconductorby epitaxial growth.

The first grown layer, in an embodiment, may be a gallium nitride layeror an aluminum nitride layer. It may also be a combination of alow-temperature buffer layer and a high-temperature buffer layer, or acombination of a buffer layer and a crystal seed layer (functioning as acrystal seed). Forming the grown layer from the low-temperature bufferlayer poses a problem that polycrystals are liable to precipitate on themask. This problem is solved by forming a crystal seed layer and thengrowing thereon a plane differing from the substrate. Thus, it ispossible to grow crystals having advantageous crystal properties. Withselective growth for crystal growing, it is necessary to grow crystalsfrom the buffer layer if there exists no crystal seed layer. Selectivegrowth from the buffer layer causes crystals to grow from the part wherethe crystal growth is not required. Consequently, the crystal seed layerpermits crystals to grow selectively in the region where crystal growthis necessary.

In an embodiment, the buffer layer is intended to relieve latticemismatch between the substrate and the nitride semiconductor. Therefore,there may be an instance where the buffer layer is not formed if thesubstrate has a lattice constant close to that of the nitridesemiconductor. For example, there may be an instance where an AlN bufferlayer is formed on SiC without lowering temperature or an AlN or GaNbuffer layer is formed on a Si substrate without lowering temperature.Thus, it is also possible to form GaN of a desirable quality. Thestructure without any buffer layer is acceptable if the substrate is GaNor a suitable material.

According to an embodiment of the present invention, the second grownlayer is formed by selective growth and consequently it is possible toobtain the slant plane, slanting to the principal plane of thesubstrate. In general, depending on the selection of the principal planeof the substrate, it is possible to form a slant plane selected from the(1–100) plane [M-plane], the (1–101) plane [S-plane], the (11–20) plane[A-plane], the (1–102) plane [R-plane], the (11–23) plane [N-plane], the(11–22) plane, the like and combinations thereof when the principalplane of the substrate is the (0001) plane [C-plane] of a wurtzitestructure.

In an embodiment, the S-plane and the (11–22) plane are preferred.Naturally, equivalent crystal planes may also be used including thosewhich have a plane orientation inclined at an angle of about 5 to about6 degrees with respect to the S-plane and the (11–22) plane. Inparticular, the S-plane is a stable plane which is obtained whenselective growth is carried out on the C+-plane. The S-plane can beobtained comparatively easily, and its index is (1–101) in the hexagonalcrystal system. Just as the C-plane includes the C+-plane and theC−-plane, the S-plane includes the S+-plane and the S−-plane. In thisspecification, the S+-plane is grown on the C+-plane GaN and it isreferred to as the S-plane unless otherwise stated. Additionally, of theS-planes, the S+-plane is stable.

When the crystal layer is formed from a gallium nitride based compoundsemiconductor, as mentioned above, the number of bonds from Ga to N is 2or 3 on the S-plane or S+-plane. This number is second to that on theC-plane. Since the C−-plane cannot be obtained on the C+-plane, inpractice, the number of bonds on the S-plane is the largest. Forexample, in the case where a nitride is grown on a sapphire substratehaving the C-plane as the principal plane, the nitride of a wurtzitestructure has a surface of C+-plane. However, it is possible to form theS-plane if selective growth is employed. On the plane parallel to theC-plane, the bond of N (which easily releases itself) combines with onebond of Ga, whereas on the inclined S-plane, it combines with at leastone bond. This causes the effective V/III ratio to increase, therebyimproving the crystal properties of the laminate structure. In addition,growth in the direction different from the orientation of the substratebends dislocations extending from the substrate, thereby favorablydecreasing defects.

According to an embodiment of the present invention, a semiconductorlight-emitting device may be constructed such that the second grownlayer by selective growth slants to the principal plane of thesubstrate. The second grown layer may be such that the S-plane (or anyother plane substantially equivalent thereto) constitutes the side facesof an approximately hexagonal pyramid, or the S-plane (or any otherplane substantially equivalent thereto) constitutes the side faces of anapproximately hexagonal prismoid and the C-plane (or any other planesubstantially equivalent thereto) constitutes the top plane of theapproximately hexagonal prismoid. The approximately hexagonal pyramid orprismoid does not necessarily need to be exactly hexagonal. It mayinclude those which have one or more missing faces. The edge between thecrystal planes of the crystal layer does not necessarily need to bestraight. Also, the approximately hexagonal pyramid or prismoid may bein an elongated shape.

In actuality, selective growth is accomplished in an embodiment by usinga selectively made opening in the masking layer formed on the firstgrown layer. The opening in the masking layer may take on any shape suchas a circle, a square, a hexagon, a triangle, a rectangle, a rhombus, astrip, a lattice, the like and combinations thereof. The masking layerin an embodiment is formed from a dielectric material such as siliconoxide, silicon nitride and the like. The masking layer may have athickness ranging from about 0.1 μm to about 5 μm (preferably from about0.1 μm to about 1.0 μm) so as to relieve steps in the vicinity of theactive layer and electrode. The approximately hexagonal pyramid orprismoid in an elongated shape may be formed if the opening (windowregion) in the masking layer is in an elongated shape.

In an embodiment, if the window region in the masking layer forselective growth is a circle of about 10 μm in diameter (or a hexagonwhose one side coincides with the (1–100) direction or (11–20)direction), it is possible to easily form a selectively grown regionwhich is about twice as large as the window region. Also, the S-plane,in a direction different from the substrate, produces the effect ofbending or isolating dislocations, thereby contributing to reduction inthe density of dislocations.

Observation by cathode luminescence on the grown hexagonal prismoidsindicates that the S-plane formed as the second grown layer hasdesirable crystal quality and is superior to the C+-plane in lightemission efficiency. Growing the InGaN active layer at about 700° C. toabout 800° C. makes ammonia decompose slowly and hence, requires morenitrogen species. Observation with an AFM revealed that the surface hasregular steps suitable for InGaN uptake. It was also found that theMg-doped layer has a good surface state owing to the S-plane and thatthe doping condition is considerably different. In general, the Mg-dopedlayer has a grown surface in a poor state when observed by an AFM.Observation by microscopic photoluminescence mapping (which has aresolving power of about 0.5 μm to about 1 μm) revealed that theS-plane, formed by selective growth, is uniform. The S-plane formed onthe C+-plane by the ordinary process has irregularities at a pitch ofabout 1 μm. Also, observation with an SEM revealed that the slope of theS-plane is smoother than that of the C+-plane.

If selective growth is carried out by using a mask such that crystalsgrow only over the opening of the mask, crystals do not grow in thelateral direction. Thus, it is possible to employ microchannel epitaxyto make crystals to grow in the lateral direction, extending beyond thewindow region. It is known that growing in the lateral direction bymicrochannel epitaxy readily avoids threading dislocations and hencereduces dislocations. Thus, growing in the lateral direction gives anenlarged light-generating region and contributes to uniform current flowand reduced current density.

A semiconductor light-emitting device according to an embodiment of thepresent invention has a cladding layer of a first conductivity type, anactive layer, and a cladding layer of a second conductivity type whichare formed parallel to the crystal plane of second grown layer. Thelayer of a first conductivity type, the active layer, and the layer of asecond conductivity type are similar to those explained in previousembodiments.

In a semiconductor light-emitting device according to an embodiment ofthe present invention, the cladding layer of a first conductivity type,the active layer, and the cladding layer of a second conductivity typeextend entirely or partly to the masking layer surrounding the opening.One advantage of the structure in which the masking layer partly remainsunremoved is that the support under the laterally grown part does notdisappear. One advantage of the structure in which the masking layerentirely remains unremoved is that a structural offset(s) or gap(s) dueto selective growth can be relieved and the masking layer functions as asupporting layer for the first grown layer, thereby keeping the n- andp-electrodes apart and preventing short-circuiting, even when thesubstrate is peeled off by laser irradiation.

Another semiconductor light-emitting device according to an embodimentof the present invention is constructed such that the second grown layeris entirely covered by the cladding layer of a first conductivity type,the active layer, and the cladding layer of a second conductivity type.This structure can be formed easily because the second grown layerassumes the slant crystal plane due to selective growth. In other words,when the active layer, parallel to the principal plane of the substrate,is formed, the end is exposed to air. However, it is possible to coverthe end by utilizing the slant crystal plane. Since the second grownlayer is entirely covered, the active layer is protected from oxidationand other degradation. Moreover, it produces the effect of increasingthe light emission area.

Further, another semiconductor light-emitting device according to anembodiment of the present invention is constructed such that each end ofthe cladding layer of a first conductivity type, the active layer, andthe cladding layer of a second conductivity type is in direct contactwith the masking layer. This structure can be formed easily because thesecond grown layer assumes the slant crystal plane due to selectivegrowth. Since each end is in direct contact with the masking layer andcovers the active layer, the active layer is previously protected fromoxidation and other degradation. Moreover, it produces the effect ofincreasing the light emission area.

A semiconductor light-emitting device according to an embodiment of thepresent invention offers improved light emission efficiency because thecrystal plane has advantageous crystal properties. The light emissionefficiency can be increased if current is injected only into the S-planehaving beneficial crystal properties owing to its desirable uptake forIn. The active layer substantially parallel to the S-plane may have anarea larger than that obtained by projecting the active layer to theprincipal plane of the substrate or the first grown layer. The activelayer, with a large area, increases the device's light emission surface,thereby leading to a reduction in current density. Moreover, the activelayer, with a large area, decreases brightness saturation and hence,increases light emission efficiency.

In an embodiment, electrodes are formed on the second grown layer andthe cladding layer of a second conductivity type, respectively. Forreduced contact resistance, the electrode may be formed on a previouslyformed contact layer. These electrodes may be formed by vapordeposition. Accurate vapor deposition is necessary to avoidshort-circuiting, which occurs as the result of the p-electrode andn-electrode coming into contact with the layer and the first grown layerformed under the mask.

A semiconductor light-emitting device according to an embodiment of thepresent invention includes a layer of a first conductivity type and alayer of a second conductivity type and an active layer which is heldbetween the layers and is formed by selective growth not parallel to theprincipal plane of the substrate for growth, with the area of the activelayer being larger than that of a window region used at the time ofselective growth on the substrate or larger than the projected areaobtained by projecting the selectively grown crystal layer to thesubstrate for growth in its normal direction. Similar concepts used inprevious embodiments will be applicable to the substrate and crystallayer, the method of forming the crystal layer, and the basicconstitution of the layer of a first conductivity type, the activelayer, and the layer of a second conductivity type.

A semiconductor light-emitting device according to an embodiment of thepresent invention is basically constructed such that the active layer isformed as a slant plane by selective growth. For the maximum effect, itis desirable that the basic device size be equal to the thickness of thecrystal grown layer or about 50 μm or less. The smaller the device size,the better the result. However, the basic structure is applicable to anydevice regardless of size so long as it is arranged one dimensionally ortwo dimensionally in a single device. In particular, a semiconductorlight-emitting device according to an embodiment of the presentinvention produces its effect when the first conductive layer with highresistance needs a high-density contact for electrodes or the secondconductive layer needs as large a contact area as possible.

In a semiconductor light-emitting device according to an embodiment ofthe present invention, the active layer is held between a layer of afirst conductivity type and a layer of a second conductivity type, andthe active layer is not parallel to the principal plane of the substratefor growth. The layer of a first conductivity type is a cladding layerof p-type or n-type, and the layer of a second conductivity type is acladding layer of an opposite type. For example, if the crystal layerhaving the C-plane is formed from a silicon-doped gallium nitride basedcompound semiconductor layer, the semiconductor light-emitting devicemay take a double heterojunction structure consisting of an n-claddinglayer of silicon-doped gallium nitride compound semiconductor, an activelayer of InGaN, and a p-type cladding layer of magnesium-doped galliumnitride based compound semiconductor which are formed sequentially oneover another. Another possible structure is such that the active layerof InGaN is held between two AlGaN layers. The active layer may be ofsingle bulk layer structure. Alternatively, it may be of single quantumwell (SQW) structure, double quantum well (DQW) structure, or multiplequantum well (MQW) structure. The quantum well structure may use abarrier layer for separation of quantum wells, if necessary. Thelight-emitting device having an active layer of InGaN is easy to produceand has desirable light emission characteristics. Moreover, InGaNreadily crystallizes with advantageous crystal properties on the S-planefrom which nitrogen atoms hardly release themselves, thereby increasingthe light emission efficiency.

Additionally, the nitride compound semiconductor tends to become n-typedue to nitrogen holes which occur in its crystal even though it is notdoped. However, it can be deliberately made n-type having a desiredcarrier density if it is doped with an ordinary donor impurity (such asSi, Ge, and Se) during crystal growth. Also, the nitride semiconductorcan be made p-type by doping with an acceptor impurity (such as Mg, Zn,C, Be, Ca, and Ba).

In an embodiment, the layer of a first conductivity type, the activelayer, and the layer of a second conductivity type are formed on thecrystal grown layer slanting to the principal plane of the substrate forgrowth. The active layer, not parallel to the principal plane of thesubstrate for growth, is easily formed by crystal growth following theformation of the slant crystal plane. If the active layer is formed onthe crystal planes extending toward both sides from the ridge line, theresulting active layer has a bent part (e.g., bending from the S-planeto C-plane or bending from the S-plane to the M-plane). When the crystalgrown layer forms an approximately hexagonal pyramid or prismoid and thesurface of the slant crystal grown layer is the S-plane, thelight-generating region (consisting of the layer of a first conductivitytype, the active layer, and the layer of a second conductivity) may beformed entirely or partly on the S-plane.

With an approximately hexagonal prismoid, it is possible to form thelayer of a first conductivity type, the active layer, and the layer of asecond conductivity type also on the plane parallel to the principalplane of the substrate, for example, on the C-plane. One advantage oflight emission by the slant S-plane is that light emerges from thesemiconductor without multiple reflection owing to the slant planes. Incontrast, with parallel planes, light attenuates due to multiplereflection. The layer of a first conductivity type (or the claddinglayer) may have the same conductivity type if it is made from the samematerial as used for the crystal layer constituting the S-plane. It isalso possible to form by controlling the density continuously after thecrystal layer constituting the S-plane has been formed. In anembodiment, the structure may be such that part of the crystal layerconstituting the S-plane functions as the layer of a first conductivitytype.

A semiconductor light-emitting device according to an embodiment of thepresent invention offers improved light emission efficiency because theslant crystal plane has desirable crystal properties. The light emissionefficiency can be increased if current is injected only into the S-planehaving desirable crystal properties owing to its advantageous uptake forIn. The active layer, substantially parallel to the S-plane, may have anarea larger than that obtained by projecting the active layer to theprincipal plane of the substrate or the underlying layer for growth. Theactive layer with a large area increases the device's emitting surface,thereby leading to a reduction in current density. Moreover, the activelayer, with a large area, decreases brightness saturation and hence,increases light emission efficiency.

In an embodiment, electrodes are formed on the crystal grown layer orthe first conductive layer and on the layer of a second conductivitytype, respectively. For reduced contact resistance, the electrodes maybe formed on a previously formed contact layer. These electrodes may beformed by vapor deposition. Accurate vapor deposition is necessary toavoid short-circuiting, which occurs as the result of the p-electrodeand n-electrode coming into contact with the crystal layer and thecrystal seed layer formed under the mask. If the fundamental structurein the present invention is applied to a light-emitting diode, theelectrodes may be formed respectively on the first and second conductivelayers. Either structure permits light to emerge from the front orreverse side as desired. In other words, either structure permits lightto emerge from the reverse side if a transparent substrate is used oreither structure permits light to emerge from the front side if atransparent electrode is used.

One feature of a semiconductor light-emitting device according to anembodiment of the present invention is that the active layer has a largearea if it is formed by selective growth on a plane not parallel to thesubstrate for growth. When the device size is limited, the currentinjection density per unit area can be reduced for the same brightnesswhen the active layer in the device has a larger effective area.Therefore, the device with a larger effective area has improvedreliability for the same brightness and increased brightness for thesame load on the active layer. In particular, if the difference betweenthe total area of the active area and the area which the selectivelygrown region occupies on the substrate for growth is larger than thearea necessary for contact with at least one electrode, then thatportion of the active layer which is limited by the contact region iscompensated. Consequently, a semiconductor light-emitting deviceaccording to an embodiment of the present invention is less likely toexperience a situation of current concentration even though its size isgreatly reduced.

In an embodiment, assuming that the crystal grown layer takes on theshape of a ridge with a triangular cross section and the slant plane ofthe crystal grown layer slants to the principal plane of the substrateat an angle of θ. It should be understood that the effective area of theactive layer is 1/cos θ times larger (at the maximum) than the projectedarea obtained by projecting the entire region of the active layer to thesubstrate for growth in its normal direction. The effective areanecessarily becomes large if the crystal grown layer is formed (in theshape of polygonal pyramid or prismoid as well as the ridge with atriangular cross section) by selective growth and then the active layeris formed thereon which is not parallel to the substrate. Additionally,the projected area is equal to the area occupied on the principal planeof the substrate and is also equal to the shadow of the crystal grownlayer which would be formed if light is projected toward the principalplane of the substrate in its normal direction.

In addition, the area of the active layer can be made larger than thearea of the substrate for growth if the region not used for crystalgrowth is minimized and the active layer is separated from its adjacentones by a growth inhibiting film (such as a masking layer) and grown tothe maximum extent such that adjacent stable planes do not come intocontact with each other. However, the maximum area attained by a singlegrowth is equal to the area of the substrate used for growth. Theeffective area of the active layer is reduced further after theelectrodes and device separating grooves have been added. Therefore, asatisfactory effect is obtained even though the total area of the activelayer is not necessarily larger than the area of the substrate forgrowth.

In an embodiment, if the effective area of the active layer is madelarger than the area of the window region used at the time of selectivegrowth on the substrate for growth, or lager than the projected areaobtained by projecting the crystal grown layer resulting from selectivegrowth to substrate in its normal direction, then it is possible toreduce the density of current injected into the active layer, therebyimproving the reliability of the device. Also, if the effective area ofthe active layer is made larger than the sum of the projected area ofthe selective grown region toward the substrate for growth in its normaldirection and the contact area of at least one electrode and theconductive layer, it is possible to reduce the density of current beinginjected into the active layer, thereby improving the reliability of thedevice. In particular, if the difference between the total area of theactive layer and the projected area of the selectively grown regiontoward the substrate for growth is larger than the area necessary forcontact with at least one electrode, then that portion of the activelayer which is limited by the contact region is compensated.

Assuming a light-emitting diode device, for example, having the size ofa 30 μm square, is produced. The region in which the first electrodecomes into contact with the underlying conductive layer (which is thefirst conductive layer) is approximately 20 μm×5 μm and the region forselective growth in which the active layer can be placed isapproximately 20 μm square at the largest. Therefore, by making thetotal area of the active layer equal to or larger than 500 μm2, it ispossible to obtain the device structure according to an embodiment ofthe present invention. If a quadrangular pyramid (with a slope angle of45° and a base side of 20 μm) is formed in the region for selectivegrowth and the active layer is formed thereon uniformly, the total areaof the active layer is 20 μm×20 μm/cos 45°=566 μm2. Thus, the effectivearea of the active layer is sufficiently large compared with the contactarea. Moreover, it is apparent that the effect will be better if theangle of the slope is larger. In view of the fact that the (1–101)stable for the (0001) of a wurtzite structure is about 62° and the (111)plane stable for the (001) plane of zincblende is about 54.7°, thepresent invention ensures satisfactory reliability by expanding theregion for the active layer.

It is possible to construct an image display unit or lighting system byarranging, in an array, a plurality of semiconductor light-emittingdevices according to an embodiment of the present invention. If devicescorresponding to three primary colors are arranged in an array capableof scanning, the resulting display unit will have a small area becausethe electrode has a reduced area owing to the use of the S-plane.

EXAMPLES

The present invention will be described in more detail with reference tothe following examples. Each example corresponds to an individualproduction process and each device resulting from the production processis a semiconductor light-emitting device having a structure definedaccording to an embodiment of the present invention. The productionprocess is described first and then the device resulting from theproduction process is subsequently described. Various modifications andchanges may be made in the semiconductor light-emitting device withoutdeparting from the spirit and scope of the invention. The followingexamples are not intended to restrict the scope of the invention.

Example 1

This example demonstrates a semiconductor light-emitting device whichhas a crystal layer formed by selective growth directly on a sapphiresubstrate. Additionally, the crystal layer includes a crystal surfacehaving the S-plane as the slant crystal plane (i.e. the crystal surfaceplane that diagonally intersects the principal plane of the substrate).Its production process and structure will be described with reference toFIGS. 3A to 9.

The sapphire substrate 10 has the C+-plane as its principal plane 11(i.e. the substrate surface plane). On the entire surface of thesapphire substrate 10 is formed the masking layer 12 (about 100 nm toabout 500 nm thick) of SiO2 or SiN. In the masking layer 12 is formedthe opening 13 (about 100 μm) by photolithography and etching withhydrofluoric acid based compound (see FIGS. 3A and 3B). In this Example,the opening 13 is in an approximately rectangular shape, but the size ofthe opening may be changed according to the characteristics of thelight-emitting device to be produced.

Then, selective growth is carried out in two stages. First, a thin GaNlayer or a low-temperature buffer layer (about 20 nm to about 30 nmthick) is grown at a low temperature of about 500° C. Secondly, thegrowing temperature is raised to about 1000° C. so as to form thesilicon-doped GaN layer 14, as shown in FIG. 4A and 4B. Thesilicon-doped GaN layer 14 grows in the opening 13 in the masking layer12, but it gradually expands in the lateral direction while it is keptat about 1000° C. in a hydrogen atmosphere.

On the silicon-doped GaN layer 14 a masking layer 15 is formed.Subsequently, an approximately round opening 16 is formed byphotolithography and etching (see FIGS. 5A and 5B). The silicon-dopedGaN layer 14 is allowed to grow further through the opening 16 until thesilicon-doped GaN layer 17 grows in the shape of a hexagonal pyramid.The surface of the crystal layer in the shape of the hexagonal pyramidis covered by the S-plane, that is, the (1–101) plane according toMiller indices of a hexagonal system. If the growing time isinsufficient or if different growing conditions are employed, thesilicon-doped GaN layer 17 may take the shape of a hexagonal prismoid inwhich the top plane is the C+-plane, parallel to the principal plane ofthe substrate. In this example, however, the silicon-doped GaN layer 17is grown until it takes the shape of a hexagonal pyramid. After thelapse of sufficient growing time, the side faces of the hexagonalpyramid of the silicon-doped GaN layer 17 are covered with the S-plane.It is necessary that the opening 16 is sufficiently apart from adjacentopenings.

It should be noted that the S-plane is intended to include one or moreof the planes relating to the family of planes corresponding to the(1–101) plane. In an embodiment, the S-plane includes the planescorresponding to each side face of the hexagonal pyramid as shown inthis example. For example, in addition to the (1–101) plane, thehexagonal pyramid has side faces corresponding to the (10–11), (01–11),(-1101), (-1011), and (0–111) planes.

After the silicon-doped GaN layer 17 has grown in the shape of ahexagonal pyramid, growing is continued until the hexagonal pyramidbecomes about 15 μm to about 20 μm wide (with one side being about 7.5μm to about 10 μm long). The height of the hexagonal pyramid is about 10μm to about 16 μm, which is about 1.6 times the side of the hexagonalpyramid. This size is merely exemplary, and the width equal to orsmaller than 10 μm may be acceptable. The silicon-doped GaN layer 17 isgrown further. Subsequently, the InGaN layer 18 is grown at a reducedgrowing temperature. The thickness of the InGaN layer 18 is about 0.5 nmto about 3 nm. Then, the magnesium-doped GaN layer 19 is grown at anincreased growing temperature, as shown in FIGS. 6A and 6B. There may bean instance where a quantum well layer (or a multiple quantum welllayer) of (Al)GaN/InGaN is formed, or there may be another instancewhere a multilayer structure is formed with GaN or InGaN functioning asthe guide layer. In such a case, it is desirable to grow the AlGaN layerdirectly on the InGaN layer.

Subsequently, etching is performed on part of the epitaxially grownlayer until the silicon-doped GaN layer 14 is exposed. In the removedpart 21, the n-electrode 20 (Ti/Al/Pt/Au) is formed by vapor deposition.On the outermost surface of the previously grown hexagonal pyramid, thep-electrode 22 (Ni/Pt/Au or Ni(Pd)/Pt/Au) is formed by vapor deposition(see FIGS. 7A and 7B). These vapor depositions should be carried outaccurately so as to prevent the p-electrode and n-electrode from cominginto contact with the silicon-doped GaN layer 17 (in the form ofhexagonal pyramid) and the silicon-doped GaN layer 14 (formed under themask), thereby preventing short-circuiting. Then, individuallight-emitting devices are separated by RIE (reactive ion etching) ordicing (i.e., separating the devices with an optical mechanism, amechanical mechanism, or the like), as shown in FIGS. 8A and 8B. Thus,the light-emitting device in this example is completed.

The light-emitting device produced by the above-mentioned process has astructure as shown in FIG. 9. It is composed mainly of the sapphiresubstrate 10 whose principal plane is the C+-plane, the silicon-dopedGaN layer 14 as a crystal seed layer, and the silicon-doped GaN layer 17as a crystal layer. The silicon-doped GaN layer 17 has the slantS-plane, slanting to the principal plane of the substrate. The InGaNlayer 18 (as an active layer) is parallel to the S-plane. On the InGaNlayer 18 is formed the magnesium-doped GaN layer 19 as a cladding layer.The p-electrode 22 is formed on the magnesium-doped GaN layer 19. Then-electrode 20 is formed in the open region at the side portion of thehexagonal pyramid, and it is connected to the silicon-doped GaN layer 17through the silicon-doped GaN layer 14.

The light-emitting device in this example has an advantage that, owingto the S-plane slanting to (i.e., diagonally intersecting) the principalplane of the substrate, the number of bonds from nitrogen atoms togallium atoms increases, which increases the effective V/III ratio.Therefore, the resulting light-emitting device has improved performance.In addition, the fact that the principal plane of the substrate is theC+-plane and hence, the S-plane is different from the principal plane ofthe substrate tends to decrease defects and dislocations extending fromthe substrate bend. The slant crystal plane slanting to the principalplane of the substrate prevents multiple reflection, thereby permittingthe generated light to emerge efficiently.

Example 2

This example demonstrates a semiconductor light-emitting device whichhas a crystal layer (having the S-plane slanting to the principal planeof the substrate) formed on a crystal seed layer isolated from asapphire substrate. Its production process and structure will bedescribed with reference to FIGS. 10A to 17B.

On the sapphire substrate 30, whose principal plane is the C+-plane, isformed a buffer layer of AlN or GaN at a low temperature of about 500°C. Then, with the temperature raised to about 1000° C., thesilicon-doped GaN layer 31 is formed. On the entire surface of thesilicon-doped GaN layer 31 is formed a masking layer (about 100 nm toabout 500 nm thick) of SiO2 or SiN. The masking layer is removed byphotolithography and etching with hydrofluoric acid based compoundexcept for the round masking part 32 (about 10 μm in diameter), as shownin FIGS. 10A and 1B. Etching is performed so that the principal plane ofthe sapphire substrate 30 is exposed, as shown in FIGS. 11A and 11B. Asa result, the cylindrical silicon-doped GaN layer 31 in conformity withthe shape of the masking part 32 remains.

Then, the masking part 32 is removed and crystal growing is againcarried out, that is, the silicon-doped GaN layer 33 is grown at araised growing temperature of about 1000° C. The silicon-doped GaN layer33 grows on the silicon-doped GaN layer 31 remaining unetched. Aftercontinued growing, the silicon-doped GaN layer 33 forms a hexagonalpyramid surrounded by the S-plane slanting to the principal plane of thesubstrate. This hexagonal pyramid grows in proportion to the growingtime. The GaN layer 31 should be sufficiently apart from adjacent layersso that the fully grown GaN layer 33 does not interfere with adjacentlayers and the completed devices are separated from each other withsufficient margins.

The hexagonal pyramid grows to such an extent that the width is about 15μm to about 20 μm (with one side being about 7.5 μm to about 15 μm long)and the height is about 10 μm to about 16 μm, which is about 1.6 timesthe side of the hexagonal pyramid, as with Example 1. This size ismerely exemplary, and the width equal to or smaller than 10 μm may beacceptable. After the hexagonal pyramid surrounded by the slant S-planehas been formed, as shown in FIGS. 12A and 12B, the silicon doped GaNlayer is grown and then the InGaN layer 34 is grown at a lower growingtemperature. Then, with the growing temperature raised, themagnesium-doped GaN layer 35 is grown, as shown in FIGS. 13A and 13B.The thickness of the InGaN layer 34 is about 0.5 nm to about 3 nm. Theremay be an instance where a quantum well layer (or a multiple quantumwell layer) of (Al)GaN/InGaN is formed, or there may be another instancewhere a multilayer structure is formed with GaN or InGaN functioning asthe guide layer. In such a case, it is desirable to grow the AlGaN layerdirectly on the InGaN layer.

The InGaN layer 34 (as an active layer) and the magnesium-doped GaNlayer 35 (as a p-type cladding layer) are partly removed at the sideclose to the substrate, so that the silicon-doped GaN layer 33 is partlyexposed. In the removed part, close to the substrate, the Ti/Al/Pt/Auelectrode (as the n-electrode 36) is formed by vapor deposition. On theoutermost surface of the hexagonal pyramid, the Ni/Pt/Au or Ni(Pd)/Pt/Auelectrode (as the p-electrode 37) is formed by vapor deposition (seeFIGS. 14A and 14B). These vapor depositions should be carried outaccurately so as to prevent the electrodes from coming into contact witheach other, thereby preventing short-circuiting, as with Example 1.

After the electrodes 36 and 37 have been formed, individuallight-emitting devices are separated by RIE (reactive ion etching) ordicing, as shown in FIGS. 15A and 15B. Thus, the light-emitting devicein this example is completed.

The light-emitting device produced by the above-mentioned process has astructure as shown in FIG. 16. It is composed mainly of the sapphiresubstrate 30 whose principal plane is the C+-plane and the silicon-dopedGaN layer 33 as a crystal layer. The silicon-doped GaN layer 33 has theslant S-plane slanting to the principal plane of the substrate. TheInGaN layer 34 (as an active layer) is parallel to the S-plane. On theInGaN layer 34 is formed the magnesium-doped GaN layer 35 as a claddinglayer. The p-electrode 37 is formed on the magnesium-doped GaN layer 35.The n-electrode 36 is formed in the open region at the vicinity of thesubstrate on the S-plane of the hexagonal pyramid, and it is connecteddirectly to the silicon-doped GaN layer 33.

The light-emitting device in this example (which is constructed asmentioned above) has an advantage that, like the light-emitting devicein Example 1, owing to the S-plane slanting to the principal plane ofthe substrate, the number of bonds from nitrogen atoms to gallium atomsincreases, which increases the effective V/III ratio. Therefore, theresulting light-emitting device has improved performance. In addition,the fact that the principal plane of the substrate is the C+-plane andhence, the S-plane is different from the principal plane of thesubstrate tends to decrease defects and dislocations extending from thesubstrate bend. The slant S-plane slanting to the principal plane of thesubstrate prevents multiple reflection, thereby permitting the generatedlight to emerge efficiently.

Additionally, in this example, the silicon-doped GaN layer is etchedfirst so that the sapphire substrate 30 is exposed. However, etching maybe carried out in such a way that a sufficiently high step is formed inthe silicon-doped GaN layer. Growing on the thus formed silicon-dopedGaN layer (as a crystal seed layer) readily gives the desired hexagonalpyramid. The device produced in this manner is shown in FIGS. 17A and17B. The step 39 is formed in the silicon-doped GaN layer 38 formed onthe sapphire substrate 30. The silicon-doped GaN layer as a crystallayer in the shape of hexagonal pyramid grows from the projection part.On the silicon-doped GaN layer are formed the InGaN layer 34 (as anactive layer), the magnesium-doped GaN layer 35 (as a p-type claddinglayer), the p-electrode 37, and the n-electrode 36. Light with a desiredwavelength is extracted from the InGaN layer 34.

Example 3

This example demonstrates a semiconductor light-emitting device in whichthe crystal layer in the shape of hexagonal pyramid (which has theS-plane slanting to the principal plane of the substrate) is formedwithin the window region for the selective mask. Its production processand structure will be described with reference to FIGS. 18A to 23.

On the sapphire substrate 40, whose principal plane is the C+-plane, isformed a buffer layer of AlN or GaN at a low temperature of about 500°C. Then, with the temperature raised to about 1000° C., thesilicon-doped GaN layer 41 is formed. On the entire surface of thesilicon-doped GaN layer 41 is formed the masking layer 42 (about 100 nmto about 500 nm thick) of SiO2 or SiN. In the masking layer 42 is formeda round opening (about 10 μm in diameter) as the window region 43 byphotolithography and etching with hydrofluoric acid based compound, asshown in FIGS. 18A and 18B. The size of the opening varies depending onthe light-emitting device desired.

Then, the silicon-doped GaN layer 44 is grown again at a growingtemperature of about 1000° C. In the beginning, the silicon-doped GaNlayer 44 grows from the round window region 43. After growing for awhile, it takes the shape of a hexagonal pyramid surrounded by S-planesor (1–101) planes. It may take the shape of a hexagonal prismoid underdifferent growing conditions. Under adequately controlled growingconditions, the silicon-doped GaN layer 44 grows until the hexagonalpyramid (covered with S-planes) almost fills the window region in theselective mask. With the growing temperature lowered, the InGaN layer 45(as an active layer) is grown. Then, the magnesium-doped GaN layer 46(as a p-type cladding layer) is grown at a raised growing temperature,as shown in FIGS. 20A and 20B. The thickness of the InGaN layer 45 isabout 0.5 nm to about 3 nm. As with Examples 1 and 2 (mentioned above),there may be an instance where a quantum well layer (or a multiplequantum well layer) of (Al)GaN/InGaN, functioning as the active layer,is formed, or there may be another instance where a multilayer structureis formed with GaN or InGaN functioning as the guide layer. In such acase, it is desirable to grow the AlGaN layer directly on the InGaNlayer. The selective growth should preferably be carried out such thatthe window region 43 of the selective mask is filled with the entirecrystal layer extending in the lateral direction. Thus, it is possibleto produce the individual light-emitting devices in uniform sizes.

Subsequently, the masking layer is partly opened so that the GaN layer41 is exposed. In the removed part 47, the Ti/Al/Pt/Au electrode (as then-electrode 48) is formed by vapor deposition. On the outermost surfaceof the hexagonal pyramid, the Ni/Pt/Au or Ni(Pd)/Pt/Au electrode (as thep-electrode 49) is formed by vapor deposition (see FIGS. 21A and 21B).These vapor depositions should be carried out accurately. Then,individual light-emitting devices are separated by RIE (reactive ionetching) or dicing, as shown in FIGS. 22A and 22B. Thus, thelight-emitting device in this example is completed.

The light-emitting device produced by the above-mentioned process has astructure as shown in FIG. 23. It is composed mainly of the sapphiresubstrate 40 whose principal plane is the C+-plane and the silicon-dopedGaN layer 44 (as a crystal layer) which has grown on the sapphiresubstrate 40 with the silicon-doped GaN layer 41 (as a crystal seedlayer) interposed between them. The silicon-doped GaN layer 44 has asurface covered with the slant S-plane slanting to the principal planeof the substrate. The InGaN layer 45 (as an active layer) is parallel tothe S-plane. On the InGaN layer 45 is formed the magnesium-doped GaNlayer 46 as a cladding layer. The p-electrode 49 is formed on themagnesium-doped GaN layer 46. The n-electrode 48 is formed in the openregion 47 at the vicinity of the hexagonal pyramid, and it is connectedto the silicon-doped GaN layer 44 through the silicon-doped GaN layer41.

As with Examples 1 and 2 (mentioned above), the light-emitting device inthis example (which is constructed as mentioned above) has an advantagethat, owing to the S-plane slanting to the principal plane of thesubstrate, the number of bonds from nitrogen atoms to gallium atomsincreases, which increases the effective V/III ratio. Therefore, theresulting light-emitting device has improved performance. In addition,the fact that the principal plane of the substrate is the C+-plane andhence, the S-plane is different from the principal plane of thesubstrate tends to decrease defects and dislocations extending from thesubstrate bend. Moreover, in this example, the selective growth islimited in the window region 43 and hence, it is easy to uniformlycontrol the size of the individual devices. The slant crystal planeslanting to the principal plane of the substrate prevents multiplereflection, thereby permitting the generated light to emergeefficiently.

Example 4

This example demonstrates a semiconductor light-emitting device in whichthe crystal layer is grown in the shape of a hexagonal pyramid largerthan the window region or the selective mask. Its production process andstructure will be described with reference to FIGS. 24A to 29.

On the sapphire substrate 50, whose principal plane is the C+-plane, isformed a low-temperature buffer layer in a manner similar to theexamples mentioned above. Then, with the temperature raised to about1000° C., the silicon-doped GaN layer 51 is formed as the first growinglayer. On the entire surface of the silicon-doped GaN layer 51 is formedthe masking layer 52 (about 100 nm to about 500 nm thick) of SiO2 orSiN. In the masking layer 52 is formed a round opening (about 10 μm indiameter) as the window region 53 by photolithography and etching withhydrofluoric acid based compound, as shown in FIGS. 24A and 24B. Thedirection of one side is perpendicular to (1–100). The size of theopening varies depending on the light-emitting device desired.

Then, the silicon-doped GaN layer 54 is grown again at a growingtemperature of about 1000° C. In the beginning, the silicon-doped GaNlayer 54 grows from the round window region 53. After growing for awhile, it takes the shape of a hexagonal pyramid surrounded by S-planesor (1–101) planes. It may take the shape of a hexagonal prismoid ifgrowing time is insufficient. After the silicon-doped GaN layer 54 hasgrown in the shape of a hexagonal pyramid, growing is continued foruntil the hexagonal pyramid becomes about 20 μm wide (with one sidebeing about 10 μm long). The height of the hexagonal pyramid is about1.6 times the side of the hexagonal pyramid. The resulting silicon-dopedGaN layer 54 is such that the base of the hexagonal pyramid extendsbeyond the window region 53 by about 16 μm, as shown in FIGS. 25A and25B. The width of about 20 μm of the hexagonal pyramid is merelyexemplary, and the width of about 10 μm may be acceptable.

The silicon-doped GaN layer is grown further. With the growingtemperature lowered, the InGaN layer 55 (as an active layer) is grown.Then, the magnesium-doped GaN layer 56 (as a p-type cladding layer) isgrown at a raised growing temperature, as shown in FIGS. 26A and 26B.The thickness of the InGaN layer 55 is about 0.5 nm to about 3 nm. Theremay be an instance where the active layer is a quantum well layer (or amultiple quantum well layer) of (Al)GaN/InGaN, or there may be anotherinstance where a multilayer structure is formed with GaN or InGaNfunctioning as the guide layer. In such a case, it is desirable to growthe AlGaN layer directly on the InGaN layer. In this stage the InGaNlayer 15 and the magnesium-doped GaN layer 56 extend over the maskinglayer 52 surrounding the window region 53, thereby entirely covering thesilicon-doped GaN layer 54 as the second grown layer. Thus, the InGaNlayer 55 (as an active layer) and the magnesium-doped GaN layer 56 haveno open ends (i.e., the ends are in direct contact with the maskinglayer 52). This prevents the active layer from oxidizing anddeteriorating.

Subsequently, the masking layer is partly opened so that the GaN layer51 is exposed. In the removed part 57, the Ti/Al/Pt/Au electrode (as then-electrode 58) is formed by vapor deposition. On the outermost surfaceof the hexagonal pyramid, the Ni/Pt/Au or Ni(Pd)/Pt/Au electrode (as thep-electrode 59) is formed by vapor deposition (see FIGS. 27A and 27B).These vapor depositions should be carried out accurately. Then,individual light-emitting devices are separated by RIE (reactive ionetching) or dicing, as shown in FIGS. 28A and 28B. Thus, thelight-emitting device in this example is completed.

The light-emitting device produced by the above-mentioned process has astructure as shown in FIG. 29. It is composed mainly of the sapphiresubstrate 50 whose principal plane is the C+-plane and the silicon-dopedGaN layer 54 (as the second grown layer) which has grown on the sapphiresubstrate 50 with the silicon-doped GaN layer 51 (as a crystal seedlayer) interposed between them. The silicon-doped GaN layer 54 has asurface covered with the slant S-plane slanting to the principal planeof the substrate. It also has a base whose area is larger than thewindow region 53.

This device has the InGaN layer 55 (as an active layer) which isparallel to the S-plane. On the InGaN layer 55 is formed themagnesium-doped GaN layer 56 as a cladding layer. The p-electrode 59 isformed on the magnesium-doped GaN layer 56. The n-electrode 58 is formedin the open region 57 at the vicinity of the hexagonal pyramid, and itis connected to the silicon-doped GaN layer 54 through the silicon-dopedGaN layer 51.

The semiconductor light-emitting device in this example, which isconstructed as mentioned above, is characterized by the silicon-dopedGaN layer 54, the InGaN layer 55, and the magnesium-doped GaN layer 56which extend entirely or partly onto the masking layer 52 surroundingthe window region 53. An advantage of this structure (with the maskremaining unremoved) is that the laterally grown part is held by asupport which does not disappear. Moreover, the masking layer 52remaining unremoved relieves steps due to the selectively grownstructure and also functions as a supporting layer for the first grownlayer 51 even when the substrate is stripped off by laser irradiation.This helps separate the n-electrode 58 and p-electrode 59 withcertainty, thereby preventing short-circuiting.

The structure of this device is characterized by the silicon-doped GaNlayer 54 which is entirely covered by the InGaN layer 55 and themagnesium-doped GaN layer 56, so that the ends of the layers 55 and 56come into direct contact with the masking layer. In other words, theycover the active layer, with their ends being in direct contact with themasking layer 52. This produces the effect of protecting the activelayer from oxidation and other deterioration while increasing the lightemission area.

The light-emitting device in this example has an advantage that, owingto the S-plane slanting to the principal plane of the substrate, thenumber of bonds from nitrogen atoms to gallium atoms increases, whichincreases the effective V/III ratio. Therefore, the resultinglight-emitting device has improved performance. In addition, the factthat the principal plane of the substrate is the C+-plane and hence, theS-plane is different from the principal plane of the substrate tends todecrease defects and dislocations extending from the substrate bend. Theslant crystal plane slanting to the principal plane of the substrateprevents multiple reflection, thereby permitting the generated light toemerge efficiently. The active layer with a large area permits currentto be injected uniformly without current concentration and also permitsthe current density to be reduced.

Example 5

This example demonstrates a semiconductor light-emitting device in whichthe p-electrode is not formed on the apex of a hexagonal pyramid of thecrystal layer with S-planes which has grown larger than the selectivemask. Its production process and structure will be described withreference to FIGS. 30A to 32.

On the sapphire substrate 50, whose principal plane is the C+-plane, isformed a low-temperature buffer layer in a manner similar to theexamples mentioned above, especially Example 4. Then, with thetemperature raised to about 1000° C., the silicon-doped GaN layer 51 isformed as the first growing layer. On the entire surface of thesilicon-doped GaN layer 51 is formed the masking layer 52 (about 100 nmto about 500 nm thick) of SiO2 or SiN. In the masking layer 52 is formeda round opening (about 10 μm in diameter) as the window region byphotolithography and etching with hydrofluoric acid based compound. Thesize of the opening varies depending on the light-emitting devicedesired.

Then, the silicon-doped GaN layer 54 is grown again at a growingtemperature of about 1000° C. In the beginning, the silicon-doped GaNlayer 54 grows from the round window region 53. After growing for awhile, it takes the shape of a hexagonal pyramid surrounded by S-planesor (1–101) planes. It may take the shape of a hexagonal prismoid ifgrowing time is insufficient. After the silicon-doped GaN layer 54 hasgrown in the shape of a hexagonal pyramid, growing is continued untilthe hexagonal pyramid becomes about 20 μm wide (with one side beingabout 10 μm long). The height of the hexagonal pyramid is about 1.6times the side of the hexagonal pyramid. The resulting silicon-doped GaNlayer 54 is such that the base of the hexagonal pyramid extends beyondthe window region 53 by about 16 μm. The width of about 20 μm of thehexagonal pyramid is merely exemplary, and the width of about 10 μm maybe acceptable.

Silicon-doped GaN is grown further. With the growing temperaturelowered, the InGaN layer 55 (as an active layer) is grown. Then, themagnesium-doped GaN layer 56 (as a p-type cladding layer) is grown at araised growing temperature. The InGaN layer 55 and the magnesium-dopedGaN layer 56 are identical with those in Example 4. In this stage, theInGaN layer 55 and the magnesium-doped GaN layer 56 extend over themasking layer 52 surrounding the window region 53, thereby entirelycovering the silicon-doped GaN layer 54 as the second growing layer.Growing in this manner prevents the InGaN layer 55 (as an active layer)and the magnesium-doped GaN layer 56 from forming open ends, therebypreventing the active layer from deteriorating.

Subsequently, the masking layer is partly opened so that the GaN layer51 on the substrate 50 is exposed. In the removed part, the Ti/Al/Pt/Auelectrode (as the n-electrode 61) is formed by vapor deposition. On theoutermost surface layer of the S-plane which has grown on the hexagonalpyramid, the Ni/Pt/Au or Ni(Pd)/Pt/Au electrode (as the p-electrode 62)is formed by vapor deposition (see FIGS. 30A and 30B). The part at whichthe p-electrode 62 is formed is one which has sufficient steps found byobservation with an AFM. In general, steps found by an AFM indicate thatthe crystal properties are comparatively poor in the vicinity of theapex of the hexagonal pyramid. This is the reason why the p-electrode 62is formed on the part excluding the apex and its vicinity. Vapordeposition to form the p-electrode 62 and n-electrode 61 should becarried out accurately so as to prevent them from coming into contactwith the silicon-doped GaN layer 54 (as a crystal layer) and thesilicon-doped GaN layer 51 (formed under the masking layer), therebypreventing short-circuiting. Then, individual light-emitting devices areseparated by RIE (reactive ion etching) or dicing (FIGS. 31A and 31B).Thus, the light-emitting device in this example is completed. Asectional view of the device is shown in FIG. 32.

The light-emitting device constructed as mentioned above ischaracterized by the silicon-doped GaN layer 54, the InGaN layer 55, andthe magnesium-doped GaN layer 56 which entirely or partly extend overthe masking layer 52 surrounding the window region 53. An advantage ofthis structure (with the mask remaining unremoved) is that the laterallygrown part is held by a support which does not disappear. Moreover, themasking layer 52 remaining unremoved relieves steps due to theselectively grown structure and also separates the n-electrode 61 andp-electrode 62 with certainty, thereby preventing short-circuiting.

The structure of this device is also characterized by the silicon-dopedGaN layer 54 which is entirely covered by the InGaN layer 55 and themagnesium-doped GaN layer 56, so that the ends of the layers 55 and 56come into direct contact with the masking layer. In other words, theycover the active layer, with their ends being in direct contact with themasking layer 52. This produces the effect of protecting the activelayer from oxidation and other deterioration while increasing the lightemission area.

Another advantage is that current injection into the active layer takesplace such that the current density is lower in the vicinity of the apexthan in the surrounding side faces, and that the part in which crystalproperties are poor is excluded from the light-generating region so asto improve the overall emission efficiency.

Example 6

This example demonstrates a semiconductor light-emitting device whichhas the n-electrode formed on the reverse side of the substrate. Itsproduction process and structure will be described with reference toFIGS. 33A to 39B.

On the sapphire substrate 50, whose principal plane is the C+-plane, alow-temperature buffer layer is formed in a manner similar to theexamples mentioned above. Then, with the temperature raised to about1000° C., the silicon-doped GaN layer 51 is formed as the first growinglayer. On the entire surface of the silicon-doped GaN layer 51 themasking layer 52 (about 100 nm to about 500 nm thick) of SiO2 or SiN isformed. In the masking layer 52 a round opening (about 10 μm indiameter) is formed as the window region by photolithography and etchingwith hydrofluoric acid based compound. The direction of one side isperpendicular to (1–100). The size of the opening varies depending onthe light-emitting device desired.

Then, the silicon-doped GaN layer 54 is grown again at a growingtemperature of about 1000° C. In the beginning, the silicon-doped GaNlayer 54 grows from the round opening. After growing for a while, ittakes the shape of a hexagonal pyramid surrounded by S-planes or (1–101)planes. It may take the shape of a hexagonal prismoid if growing time isinsufficient. After the silicon-doped GaN layer 54 has grown in theshape of a hexagonal pyramid, growing is continued until the base of thehexagonal pyramid extends about 16 μm beyond the window region.

The silicon-doped GaN layer is grown further. With the growingtemperature lowered, the InGaN layer 55 (as an active layer) is grown.Then, the magnesium-doped GaN layer 56 (as a p-type cladding layer) isgrown at a raised growing temperature. The InGaN layer 55 and themagnesium-doped GaN layer 56 are identical to those described in Example4. In this stage, the InGaN layer 55 and the magnesium-doped GaN layer56 extend over the masking layer 52 surrounding the window region,thereby entirely covering the silicon-doped GaN layer 54 as the secondgrowing layer. Growing the layers in this manner prevents the InGaNlayer 55 (as an active layer) and the magnesium-doped GaN layer 56 fromforming open ends, thereby preventing the active layer fromdeteriorating.

As shown in FIGS. 33A and 33B, the p-electrode 71 is formed on theoutermost S-plane of the magnesium-doped GaN layer 56 before forming ofan n-electrode. The separating grooves 72 reaching the principal planeof the sapphire substrate 50 are formed by RIE or dicing. Individualdevices are separated from one another on the sapphire substrate 50 (seeFIGS. 34A and 34B). The part constituting the device is separated fromthe sapphire substrate 50 by excimer laser. Residual Ga, for example, isremoved by etching. On the reverse side of the device, the Ti/Al/Pt/Auelectrode is formed by vapor deposition. This electrode functions as then-electrode 73, as shown in FIGS. 35A and 35B.

FIGS. 36A–36C show another method of forming the n-electrode on thereverse side. This method employs a second sapphire substrate 77, whichis coated with an adhesive layer 78 and a resin layer 79. The devicesshown in FIGS. 33A and 33B are embedded in the resin layer 79.Subsequently, the sapphire substrate 50 is removed by laser abrasion, asshown in FIG. 36A. An excimer laser (with a wavelength of about 248 nm)may be used for this purpose.

Residual Ga remaining on the surface is removed. On the surface fromwhich the sapphire substrate 50 has been removed is formed the mask M(such as a Ni mask), as shown in FIG. 36B. Individual devices areseparated from one another by RIE with a chlorine based gas or the like.The mask M is removed, and the electrode 76 of Ti/Pt/Au or Ti/Au isformed on the reverse side of the device.

FIG. 37 is a sectional view showing the completed semiconductorlight-emitting device. The n-electrode 73 should be arranged near thecorners so that it does not interrupt light. FIG. 38 shows the reverseside of the completed semiconductor light-emitting device. It should benoted that the n-electrode 74 has the hexagonal opening 75 whichcoincides with the hexagonal base of the silicon-doped GaN layer 54 asthe second growing layer, thereby permitting generated light to beextracted efficiently.

This example may be modified such that the n-electrode is a transparentelectrode. FIGS. 39A and 39B show a light-emitting device in which theregion corresponding to the device is removed from the substrate byusing excimer laser, for example, and the transparent electrode 76 isformed on the reverse side of the device. Additionally, the device hasthe same structure as shown in FIG. 37. Thus, the masking layer 52remaining on the silicon-doped GaN layer 51 has the window region fromwhich the hexagonal pyramid grows, which is composed of thesilicon-doped GaN layer 54, the InGaN layer 55, and the magnesium-dopedGaN layer 56, with the p-electrode 71 formed on the outermost layer. Thetransparent electrode 76 is formed from ITO (indium tin oxide) bylift-off technique on the reverse side of the silicon-doped GaN layer 51from which the substrate has been stripped off. Lift-off techniqueinvolves, for example, peeling away the unwanted metal and leavingbehind metal traces where desired.

FIG. 40 is a sectional view showing the completed semiconductorlight-emitting device having the transparent electrode 76. Thetransparent electrode 76 transmits light generated by the InGaN layer 55(as an active layer) which is held between the silicon-doped GaN layer54 and the magnesium-doped GaN layer 56. An advantage of this structure(with the masking layer 52 remaining) is that the laterally grown partis held by a support which does not disappear. Moreover, the maskinglayer 52 relieves steps due to the selectively grown structure and alsokeeps the p-electrode 71 and the transparent electrode 76 apart, therebypreventing short-circuiting, even when the substrate is stripped off bylaser irradiation, for example. In addition, the fact that lightgenerated by the active layer emerges through the transparent electrode76 makes it unnecessary for the optical path to circumvent theelectrode. Thus, another advantage is easy production and improved lightemergence efficiency (i.e., the structure that permits light to emergefrom the reverse side of the silicon-doped GaN layer 51 also permitslight to emerge, which has been reflected by the slant crystal planes).Since the p-electrode 71 is arranged near the apex of the hexagonalpyramid, it is possible to form the transparent electrode 76 over acomparatively large area on the reverse side of the silicon-doped GaNlayer 51, thereby reducing the contact resistance of the transparentelectrode 76 and obviating the necessity of fabricating the maskinglayer for the n-electrode lead. Therefore, the device in this examplecan be produced easily.

Example 7

This example demonstrates a semiconductor light-emitting device which isproduced by selective growth from an elongated window region. Itsproduction process and structure is described with reference to FIGS. 41to 44.

First, on the sapphire substrate 80, whose principal plane is theC+-plane, a buffer layer of AlN or GaN is formed at a low temperature ofabout 500° C., as shown in FIG. 41. Then, with the temperature raised toabout 1000° C., the silicon-doped GaN layer 81 is formed. On the entiresurface of the silicon GaN layer 81 the masking layer 82 (about 100 nmto about 500 nm thick) is formed of SiO2 or SiN. In the masking layer82, the window region 83 (i.e., a rectangular opening measuring about 10μm×about 50 μm) is formed by photolithography and etching withhydrofluoric acid based compound. The long side of the opening alignswith the (1–100) direction. Then, with the temperature raised to about1000° C., crystal growing is carried out once again to form thesilicon-doped GaN layer 84. The silicon-doped GaN layer 84 grows in thewindow region 83 in the masking layer, but it takes a hexagonal shapesimilar to a ship's bottom after continued growing, as shown in FIG. 42.The surface of the hexagonal structure is covered with the S-plane.

When the top C-plane has become almost flat or has disappeared after thelapse of sufficient time, the silicon-doped GaN layer is grown further.With the growing temperature lowered, the InGaN layer 85 (as an activelayer) is grown. Then, with the growing temperature raised again, themagnesium-doped GaN layer 86 (as a p-type cladding layer) is grown. Thethickness of the InGaN layer 85 is about 0.5 nm to about 3 nm. As inExamples 1 and 2 (mentioned above), there may be an instance where aquantum well layer (or a multiple quantum well layer) of (Al)GaN/InGaN,functioning as the active layer, is formed, or there may be anotherinstance where a multilayer structure is formed with GaN or InGaNfunctioning as the guide layer. In such a case, it is desirable to growthe AlGaN layer directly on the InGaN layer.

Subsequently, the masking layer is partly opened so that the GaN layer81 is exposed. In the removed part, the n-electrode 87 of Ti/Al/Pt/Au isformed by vapor deposition. On the outermost surface of the previouslygrown layers, the p-electrode 88 of Ni/Pt/Au or Ni(Pd)/Pt/Au by vapordeposition (FIG. 43). These vapor depositions should be carried outaccurately. Subsequently, individual light-emitting devices areseparated by RIE (reactive ion etching) or dicing. Thus, thelight-emitting device in this example is completed.

The light-emitting device produced by the above-mentioned process has astructure as shown in FIG. 44. It is characterized by the silicon-dopedGaN layer 84 which possesses the S-plane as well as the (11–22) plane,thereby permitting the active region to be formed over a large area. Theeffect of this structure is uniform current flow without currentconcentration and reduced current density.

Example 8

This example demonstrates a semiconductor light-emitting device in whichthe crystal layer is a hexagonal prismoid larger than the selective maskor window region. Its production process and structure will be describedwith reference to FIGS. 45A to 50.

First, on the sapphire substrate 90, whose principal plane is theC+-plane, a low-temperature buffer layer is formed in a manner similarto the examples mentioned above. Then, with the temperature raised toabout 1000° C., the silicon-doped GaN layer 91 is formed. On the entiresurface of the silicon-doped GaN layer 91, the masking layer 92 (about100 nm to about 500 nm thick) is formed of SiO2 or SiN. In the maskinglayer 92, the window region 93 (or a round opening about 10 μm indiameter) is formed by photolithography and etching with hydrofluoricacid based compound, as shown in FIGS. 45A to 45B. The size of theopening varies depending on the light-emitting device desired.

Then, with the temperature raised to about 1000° C., crystal growing iscarried out once again to form the silicon-doped GaN layer 94. Thesilicon-doped GaN layer 94 grows in the window region 93, but it takesthe shape of a hexagonal prismoid, whose side plane is the S-plane(1–101) and whose top plane is the C-plane parallel to the principalplane of the substrate, after continued growing. Crystal growing iscarried out for a sufficient length of time so that the silicon-dopedGaN layer 94 takes the shape of a hexagonal prismoid whose top C-planeis flat (see FIGS. 46A to 46B). This prismoid forms in a shorter timethan the above-mentioned hexagonal pyramid.

The growing of the silicon-doped GaN is continued. With the growingtemperature lowered, the InGaN layer 95 (as an active layer) is grown.Then, with the growing temperature raised again, the magnesium-doped GaNlayer 96 (as a p-type cladding layer) is grown, as shown in FIGS. 47A to47B. The thickness of the InGaN layer 95 is about 0.5 nm to about 3 nm.As with the examples, mentioned above, there may be an instance where aquantum well layer or a multiple quantum well layer is formed, or wherea guide layer is formed.

Subsequently, the masking layer is partly opened so that the GaN layer91 is exposed. In the removed part 97, the n-electrode 98 of Ti/Al/Pt/Auis formed by vapor deposition. On the outermost surface of thepreviously grown pyramid, the p-electrode 99 of Ni/Pt/Au or Ni(Pd)/Pt/Auis formed by vapor deposition (see FIGS. 48A to 48B). As mentionedabove, these vapor depositions should be carried out accurately. Then,individual light-emitting devices are separated by RIE (reactive ionetching) or dicing, as shown in FIGS. 49A to 49B. Thus, thelight-emitting device in this example is completed.

The light-emitting device produced by the above-mentioned process has astructure as shown in FIG. 50. It is characterized by the sapphiresubstrate 90 which has the C+-plane as its principal plane and thesilicon-doped GaN layer 94 formed thereon which takes the shape of ahexagonal prismoid with a flat top. The hexagonal prismoid lacks theapex part in which the crystal properties are poor. Therefore, thisstructure prevents loss in light emission characteristics. Moreover, thefact that the hexagonal prismoid is formed in a comparatively short timeis also desirable for the process.

The structure, having all or part of the silicon-doped GaN layer 94, theInGaN layer 95, and the magnesium-doped GaN layer 96 extending over themasking layer 92 around the window region 93, with the mask remainingunremoved, relieves steps due to the selective growth and separates then-electrode 98 and p-electrode 99 with certainty, thereby preventingshort-circuiting. An alternative structure is possible in which the endsof the InGaN layer 35 and the magnesium-doped GaN layer 36 are in directcontact with the masking layer 92. Consequently, all the ends come intodirect contact with the masking layer 32, thereby covering the activelayer, thereby protecting the active layer from oxidation and otherdeterioration while also increasing the light emission area.

FIGS. 51 and 52 show another structure of the semiconductorlight-emitting device of hexagonal prismoid structure. FIGS. 51A to 51Bis a diagram showing the process of forming the electrode of the device.The semiconductor light-emitting device shown in FIGS. 51 and 52 is amodified example of the semiconductor light-emitting device shown inFIG. 50. It is characterized by the sapphire substrate 90 which isremoved by irradiation with excimer laser and the n-electrode 98 b whichis formed on the reverse side of the silicon-doped GaN layer 91. On thegrown layer, in the shape of hexagonal prismoid with a flat top are thesilicon-doped GaN layer 94, the InGaN layer 95, and the magnesium-dopedGaN layer 96 which entirely or partly extend to the masking layer 92around the window region. On the outermost layer of them, thep-electrode 99 is formed.

The structure shown in FIGS. 51A, 51B and 52 is characterized by then-electrode 98 b which is formed on the reverse side of thesilicon-doped GaN layer 91 outside the window region in the maskinglayer 92 through which light emerges. An advantage of this structure isthat the size of the semiconductor light-emitting device is reduced andit is not necessary to form the contact region by opening the maskinglayer 92. This is convenient to production and size reduction. Also inthe semiconductor light-emitting device of a hexagonal prismoidstructure, the n-electrode 98 b may be replaced by a transparentelectrode of ITO film, thereby increasing the contact area andsimplifying the manufacturing process.

Example 9

This example demonstrates a semiconductor light-emitting device in whichthe p-electrode is formed such that the surface of the substrateoccupies a large area. Its production process and structure will bedescribed with reference to FIGS. 53A and 53B.

The process in this example is the same as that described in Example 6up to the stage in which the magnesium-doped GaN layer 56 is grown.Therefore, the parts involved up to this stage are given the samereference numerals but their explanation is omitted.

An opening is made in the masking layer 52 on the sapphire substrate 50.This opening is close to one side of the substrate 50. In this opening,the n-electrode 100 of Ti/Al/Pt/Au is formed by vapor deposition. Thisn-electrode 100 supplies current to the region composed of a pluralityof hexagonal pyramids. The p-electrode 101 of Ni/Pt/Au or Ni(Pd)/Pt/Auis formed by vapor deposition. The p-electrode 101, covering a largearea, permits each device to emit strong light. These devices functionas a lighting system if they are given the same potential, or thesedevices function as an image display unit if the p-electrodes 101 aregiven independent signals. Moreover, these devices constitute amulticolor or full-color image display unit if they are so arranged asto correspond to the three primary colors. The image display unit orlighting system may be constructed of the above-mentioned devices onlyor a mixture of the above-mentioned devices and other devices producedin different ways.

All or part of the silicon-doped GaN layer 54, the InGaN layer 55, andthe magnesium-doped GaN layer 56 extend to the masking layer 52 aroundthe window region 53. The mask remaining unremoved relieves steps due tothe selective growth and also separates the n-electrode 100 andp-electrode 101 from each other with certainty, thereby preventingshort-circuiting. Another structure is also possible in which the InGaNlayer 55 and the magnesium-doped GaN layer 56 come into direct contactwith the masking layer 52. The advantage of this structure is that thelayers' ends in direct contact with the masking layer 52 cover theactive layer, thereby protecting the active layer from oxidation andother deterioration. Another advantage is an increased light emissionarea.

Example 10

This example demonstrates an image display unit or a lighting systemconstructed of the semiconductor light-emitting devices obtained in theabove-mentioned examples which are so arranged as to suit a simplematrix drive, as shown in FIG. 54. Each semiconductor light-emittingdevice is arranged, on the substrate 120, in such a manner that itsregion emitting red color, its region emitting blue color, and itsregion emitting green color are provided linearly. They are suppliedwith current through respective wires 126R, 126G, and 126B which areconnected to the respective p-electrodes 124. The n-electrode 122 is acommon electrode. If necessary, selective transistors may be formed tocontrol pixels individually. The masking layer 125 remains on thesubstrate 120, so that it relieves steps on its underlying silicon-dopedGaN layer 121.

The semiconductor light-emitting devices in each row for red color, bluecolor, and green color have active layers which are capable of emittinglight with a first, second, and third wavelength, respectively. Thedevices will function as an image display unit for two-dimensionalimages if the wires 126R, 126G, and 126B are given signalsindependently. The devices will function as a lighting system if thewires 126R, 126G, and 126B are given identical signals.

Additionally, the process in the foregoing examples consists of forminga low-temperature buffer layer on the sapphire substrate, growing theGaN layer, forming the selective mask, and performing selective growth.The process may be so modified as to form the GaN layer directly on Siat about 900° C., or to form an AlN layer (5 nm thick) on Si at about1000° C. and then grow GaN, or to use the GaN substrate and subsequentlyform the selective mask.

Example 11

This example demonstrates a semiconductor light-emitting device whichhas on a substrate for growth 131, with the C-plane (i.e. the (0001)plane), (for example, a sapphire substrate), an n-type GaN layer 132 (asan underlying layer for growth) grown by MOCVD, MOVPE or the like and amasking layer 133 (as a growth inhibiting film of silicon oxide, siliconnitride, or tungsten).

In the masking layer 133, a window region 134 which has a hexagonalopening is formed. In the window region 134, the crystal grown layer 135(having a triangular cross section) is formed by selective growth. Thecrystal grown layer 135 is an n-type GaN layer or an AlGaN layer, forexample, and has a cross section of an approximately regular triangle.It is hexagonal when viewed from above, and it takes the shape of ahexagonal pyramid as a whole.

The crystal grown layer 135 has side faces (which are the S-plane or anequivalent thereof) slanting to the principal plane of the substrate. Onthe crystal grown layer 135 is an n-type cladding layer with acontrolled concentration, for example. On the n-type cladding layer areformed the active layer 136 and the second conductive layer 137 (whichfunctions as a p-type cladding layer). The active layer 136 and thesecond conductive layer 137 are formed to cover the S-plane of thecrystal grown layer 135. The active layer 136 is grown along the S-planeof the crystal grown layer 135, and it is not parallel to the principalplane of the substrate 131. The second conductive layer 137 is a p-typeGaN layer or an AlGaN layer. An AlGaN layer may be formed on the activelayer 136.

On the second conductive layer 137, the second electrode 139 (whichfunctions as a p-electrode) is formed in the form of multi-layer metalfilm of Ni/Pt/Au or Ni(Pd)/Pt/Au. In the opening in the masking layer133, the first electrode 138 (which functions as an n-electrode) isformed in the form of a multi-layer metal film of Ti/Al/Pt/Au, forexample. The first electrode 138 and the second electrode 139 may beformed by vapor deposition, lift-off technique, or the like.

An advantage of the semiconductor light-emitting device in this exampleis that the active layer 136 has a large area functioning to relieve thecurrent density injected into the active layer 136. In particular, thearea S of the active layer 6 is sufficiently large because the activelayer 136 extends along the S-plane of the crystal grown layer 135, notparallel to the principal plane of the substrate for growth 131. Thearea S of the active layer 6 may be larger than the sum of S1 and S2,where S2 is the area of the first electrode 138 and S1 is the area ofthe crystal grown layer 135 projected to the principal plane of thesubstrate, as shown in FIG. 55.

In the case where the device in this example is a light-emitting diodehaving the size of, for example, a 30 μm square, the area of S2 is about20 μm×about 5 μm or about 100 μm2 and the area of S1 is about 20μm×about 20 μm or about 400 μm2 at the largest. S2 is the region inwhich the first electrode comes into contact with the underlyingconductive layer as the first conductive layer, and S1 is the projectedregion of the active layer. Therefore, by making the total area of theactive layer equal to or larger than about 500 μm2 (i.e., S1+S2), it ispossible to obtain the device structure according to the presentinvention.

Conversely, where the crystal grown layer 135 formed by selective growthis a quadrangular pyramid whose base is about a 20 μm square and whoseside faces are formed at an angle of 45°, the total area of the activelayer 136 which is uniformly formed on the side faces is about 20μm×about 20 μm/cos 45° or about 566 μm2 (i.e., clearly bigger than about500 μm2). The area S of the active layer increases even more when it isformed on the S-plane of a hexagonal pyramid (with an angle of about62°).

FIGS. 56 and 57 show that when the area S of the active layer 136 isincreased to relieve the brightness saturation, it becomes larger thanthe area W1 of the window region 133 (see FIG. 56) or the area W2 of thecrystal grown layer projected to the principal plane of the substrate inits normal direction (see FIG. 57). When the active layer 136 extendsalong the S-plane of the crystal grown layer 135, not parallel to theprincipal plane of the substrate 131, the area S of the active layer 136becomes larger than the area W1 or the projected area W2. In otherwords, the active layer 136 has a sufficient area, thereby effectivelyrelieving brightness saturation and improving device reliability.

The light-emitting device constructed as shown in FIG. 55 offers anadvantage that, in addition to the effect produced by the increased areaof the active layer, the S-plane slanting to the principal plane of thesubstrate increases the number of bonds from nitrogen atoms to galliumatoms, thereby increasing the effective V/III ratio. Therefore, theresulting light-emitting device has improved performance. In addition,dislocations extending from the substrate bend and defects tend todecrease. The slant crystal plane slanting to the principal plane of thesubstrate prevents multiple reflection, thereby permitting the generatedlight to emerge efficiently. The structure in which the active layers136 are isolated from one another obviates the necessity of etching theactive layer 136, thereby eliminating damage to the active layers.Another advantage is that the effective area of the active layer 136 isnot reduced by the electrode.

Example 12

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 154 is formed in a stripe pattern on thesubstrate 150, as shown in FIG. 58. The semiconductor light-emittingdevice consists of the substrate for growth 150, the underlying layerfor growth 151, the masking layer 152, and the crystal grown layer 154in a stripe pattern which is formed in the window region in the maskinglayer 152. The crystal grown layer 154 has the side face 156 which isthe S-plane. The active layer 155 is extendingly formed also on theslant side face 156, so that the area of the active layer 155 is largerthan the projected area of the crystal grown layer 154, therebyeffectively relieving brightness saturation and improving devicereliability.

Example 13

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 164 is formed in the shape of an elongatedquadrangular prismoid on the substrate 160, as shown in FIG. 59. Thesemiconductor light-emitting device consists of the substrate for growth160, the underlying layer for growth 161, the masking layer 162, and thecrystal grown layer 164 formed in the shape of a stripe and an elongatedquadrangular prismoid in the window region in the masking layer 162. Thecrystal grown layer 164 has the side face 163S which is the S-plane. Theface 164 at the end in the lengthwise direction is the (11–22) plane.The top face 163C of the crystal grown layer 164 is the C-plane which isidentical with the principal plane of the substrate. The active layer,which is not shown, extends over the slant side face 163S, the face 164,and the top face 163C, so that the area of the active layer is largerthan the projected area of the crystal grown layer 164, therebyeffectively relieving brightness saturation and improving devicereliability.

Example 14

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 174 is formed in the shape of a quadrangulartrapezoid on the substrate for growth 170, as shown in FIG. 60. Thesemiconductor light-emitting device consists of the substrate for growth170, the underlying layer for growth 171, the masking layer 172, and thecrystal grown layer 173 which is formed in the shape of a quadrangularprismoid in the window region in the masking layer 172. The quadrangularprismoids are arranged in a matrix pattern. The crystal grown layer 173has the slant side face 173S which is the S-plane and the other sideface 174 which is the (11–22) plane. The top plane 173C of the crystalgrown layer 173 is the C-plane which is identical (i.e. parallel) to theprincipal plane of the substrate. The active layer, which is not shown,extends over the slant side face 173S, the face 174, and the top face173C, so that the area of the active layer is larger than the projectedarea of the crystal grown layer 173, thereby effectively relievingbrightness saturation and improving device reliability.

Example 15

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 183 is formed in the shape of a hexagonalpyramid on the substrate for growth 180, as shown in FIG. 61. Thesemiconductor light-emitting device consists of the substrate for growth180, the underlying layer for growth 181, the masking layer 182, and thecrystal grown layer 183 which is formed in the shape of a hexagonalpyramid in the window region in the masking layer 182. The hexagonalpyramids are arranged in a matrix pattern. The crystal grown layer 183has the slant side face which is the S-plane. The active layer, which isnot shown, extends over the slant S-plane, so that the area of theactive layer is larger than the projected area of the crystal grownlayer 183. Refer to FIG. 55 and Example 11, for example, for adiscussion regarding the relationship of the area of the active layerand the projected area of the crystal grown layer. This structureeffectively relieves brightness saturation and improves devicereliability.

Example 16

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 193 is formed in the shape of a hexagonalprismoid is formed on the substrate for growth 190, as shown in FIG. 62.The semiconductor light-emitting device consists of the substrate forgrowth 190, the underlying layer for growth 191, the masking layer 192,and the crystal grown layer 193 which is formed in the shape of ahexagonal prismoid in the window region in the masking layer 192. Thehexagonal prismoids are arranged in a matrix pattern. The crystal grownlayer 193 has the slant side face 193S which is the S-plane, and alsohas the top face 193C which is the C-plane identical to the principalplane of the substrate. The base of the hexagonal pyramid is the M-planeor the (1–100) plane at the low position (i.e. the crystal grown layerhaving the S-plane as a side face bends to encompass the M-plane at thebase of the hexagonal pyramid). The active layer, which is not shown,extends over the slant S-plane and the C-plane, so that the area of theactive layer is larger than the projected area of the crystal grownlayer 193. This structure effectively relieves brightness saturation andimproves device reliability.

Example 17

This example demonstrates the process for producing the semiconductorlight-emitting device shown in FIG. 55. The process is described withreference to FIGS. 63 to 68.

On the substrate for growth 200 (for example, a sapphire substrate) then-type GaN layer 201 (as an underlying layer for growth) is formed byMOCVD or the like, as shown in FIG. 63. The n-type GaN layer 201 needsnot be n-type initially. However, it is acceptable so long as itsuppermost face is n-type. The desired n-type GaN layer 201 may be formedby doping with silicon, for instance.

On the entire surface of the n-type GaN layer 201 the masking layer 202is formed by CVD or the like, as shown in FIG. 64. The masking layer 202is a silicon oxide film, silicon nitride film, tungsten film, or thelike which functions as a growth inhibiting film. The masking layer 202is partly removed to form a plurality of hexagonal window regions 203corresponding to the regions in which the devices are formed.

Selective growth is carried out so as to form the n-type (Al)GaN layer204 as the crystal grown layer in the window region 203, as shown inFIG. 65. This n-type (Al)GaN layer 204 also functions as a claddinglayer, and it takes the shape of an approximately hexagonal pyramid. Theslant side face is the S-plane.

On the slant side face are formed the InGaN layer 205 (as an activelayer) and the p-type (Al)GaN layer 206, as shown in FIG. 66. The InGaNlayer 205 as an active layer extends broadly over the S-plane of the(Al)GaN layer 204 as the crystal grown layer, not parallel to theprincipal plane of the substrate for growth. The area S of the activelayer is larger than the area of the window region 203 and the projectedarea of the crystal grown layer. It is possible to form an AlGaN layeron the InGaN layer 205.

When poly-GaN or the like is grown on the masking layer, unnecessaryparts are removed by etching. The masking layer 202 is removed partly orentirely to form the n-side contact region 207, as shown in FIG. 67. Thep-electrode 209 of Ni/Pt/Au or Ni(Pd)/Pt/Au is formed by vapordeposition or the like. The n-electrode 78 of Ti/Al/Pt/Au is formed inthe contact region 207 by lift-off technique or the like (see FIG. 68).After alloying, the device on the substrate is completed.

The basic structures of the individual devices are so small that it isdifficult to separate them from one another. However, it is onlynecessary to separate them into groups by dicing, cleavage and the like,each group consisting of devices arranged in one dimension or twodimensions. The internal basic structures of individual devices in eachgroup may or may not be driven independently. The GaN crystals grown onthe sapphire substrate can be peeled off from the sapphire substrate ifthe sapphire/GaN interface is subjected to UV laser abrasion through thesapphire, as reported by W. S. Wong et al. in APL-75-10, 1360-2. If thefirst grown film (the first conductive film) is removed by etchingbefore or after laser abrasion, it is possible to form a singlesemiconductor light-emitting device having the basic structure accordingto an embodiment of the present invention.

As mentioned above, the process in this example offers the advantagethat the S-plane can be formed easily by selective growth and the activelayer can be formed on the crystal grown layer whose side face is theS-plane, thereby obtaining the active layer with a large area.

Example 18

This example demonstrates a semiconductor light-emitting device havingthe structure as shown in FIG. 69. The device includes the substrate forgrowth 210, the second grown layer 211, the first conductive layer 211(covering the second grown layer 211), the active layer 213, and thesecond conductive layer 219. Although there is not a masking layer orwindow regions, the area of the active layer 213 is made larger, byselective growth, than the projected area of the crystal grown layer,thereby effectively relieving brightness saturation and improving devicereliability. In other words, even in the case where a growth inhibitingfilm (such as a masking layer) is not used, it is possible to form astable plane and produce the same effect as that which would be obtainedby forming a growth inhibiting film, if microfabrication is carried outby etching (for example, surface irregularities are formed on thesubstrate for growth or the crystal film which has been grownpreviously).

Additionally, according to an embodiment of the present invention, ahexagonal opening is most desirable as the window region in which thehexagonal pyramid is grown. However, the shape of the opening or thedirection of the boundary of the opening is arbitrary because the stableplane is eventually formed by itself even in the case of a roundopening. The present invention is applicable also to the structure inwhich the stable plane, such as the (11–22) plane and the (1–100) planeother than the (1–101) plane in a wurtzite crystal, is formed by itself.

At present, red LEDs are usually made from an AlGaInP compound ofzincblende structure. This compound has stable planes such as the (011)plane, the (111) plane, and the (11–1) plane with respect to the (001)substrate. If it is grown under adequate conditions, it is possible toform the stable plane and the active layer thereon.

Example 19

This example demonstrates a semiconductor light-emitting device as shownin FIG. 70, which is formed in the following manner. On substrate forgrowth 221 such as a sapphire substrate with the C-plane (i.e. the(0001) plane) the underlying layer 222 (which is an n-type GaN layer) isformed by MOCVD, MOVPE or the like.

On the underlying layer for growth 222, the masking layer 223 is formedas a growth inhibiting film, for example, a silicon oxide film, asilicon nitride film, a tungsten film, the line and combination thereof.In the masking layer 223, the window region 224 is formed as a hexagonalopening. In this window region 224, the crystal grown layer 225 isformed by selective growth, thereby obtaining a shape with a triangularcross section. This crystal grown layer 225 is an n-type GaN layer orAlGaN layer and has a cross section of an approximately regulartriangle. It is hexagonal when viewed from above and it takes the shapeof a hexagonal pyramid as a whole.

The crystal grown layer 225 has the crystal plane (or the S-plane or aplane equivalent thereto) slanting to the principal plane of thesubstrate. On the crystal grown layer 225, an n-type cladding layer isformed by adjusting the concentration of the outermost portion of thecrystal grown layer 225. On the n-type cladding layer are formed theactive layer 226 and the second conductive layer 227 (which functions asa p-type cladding layer). The active layer 226 and the second conductivelayer 227 (which functions as a p-type cladding layer) are so formed asto cover the S-plane of the crystal grown layer 225. The active layer226 is grown along the S-plane of the crystal grown layer 225 and it isnot parallel to the principal plane of the substrate for growth 221. Thesecond conductive layer 227 is a p-type GaN layer or an AlGaN layer. AnAlGaN gap layer may be formed on the active layer 226. In this example,the surface of the second conductive layer 227 becomes the interfacewith the second electrode to be formed subsequently, and this interfacefunctions as the reflecting plane 240 for light generated by the activelayer 226.

On the second conductive layer 227, the second electrode (not shown inFIG. 70, which functions as a p-electrode), is formed in the form of amulti-layer metal film of Ni/Pt/Au. In the opening in the masking layer,the first electrode, which functions as an n-electrode, is formed in theform of a multi-layer metal film of Ti/Al/Pt/Au. The first and secondelectrodes may be formed by vapor deposition, lift-off technique or thelike.

The semiconductor light-emitting device in this example is characterizedby enabling part of the light generated within to emerge afterreflection by the reflecting plane 240 which is parallel to the slantcrystal plane. Since reflection improves the light emergence efficiency,the semiconductor light-emitting device has increased brightness.Moreover, the reflecting plane 240 is formed on the slant crystal planewhich can be readily formed by itself by selective growth withoutadditional etching.

FIG. 71 is a sectional view showing major parts of the semiconductorlight-emitting device. The device has its substrate for growth removedby irradiation with excimer laser through the reverse side, so that thebottom of the underlying layer for growth 222 functions as the lightemerging window 228. The underlying layer for growth 222 is asilicon-doped GaN layer, which is connected to an n-electrode (notshown). As shown in FIG. 70, the light generated by the active layer 226advances to the second conductive layer 227 to be reflected by thereflecting plane 240, and it eventually emerges from the light emergingwindow 228. The light generated by the active layer 226 also advances tothe light emerging window 228. Thus, the light undergoes totalreflection and is directed to the reflecting plane 240. The reflectedlight advances along the optical path altered on the basis of arelationship of a reflection angle to an incident angle, and emergesfrom the light emerging window 228 if the angle of incidence is smallerthan the critical angle.

The mechanism of reflection will be explained in more detail below. Therefractive index in the device is larger than that in the outside.Therefore, light with a large incident angle to the interfaceexperiences total reflection. The condition of total reflection is asfollows.øc=sin−1(n1/n2)(where, øc denotes the critical incident angle to the interface, and n1and n2 respectively denote the refractive index of the outside and theinside: For example, øc is 24.6° when n1 is equal to 1 and n2 is equalto 2.4.

With the semiconductor light-emitting device constructed as shown inFIG. 1, a portion of the light generated by the active layer experiencestotal reflection by the window region and that portion of lightexperiences total reflection repeatedly, without emerging from thewindow. This does not occur in a semiconductor device made pursuant toan embodiment of the present invention because the reflecting plane 240is inclined so that that a portion of the light which has experiencedtotal reflection is reflected again by the reflecting plane and returnedalong the different optical path not involved with total reflection.Thus, the light emerges from the window, therefore improving lightemergence efficiency and increasing brightness. Consequently, thesemiconductor light-emitting device in this example has improved lightemergence efficiency and high brightness.

FIGS. 72 to 76 illustrate the results of simulation of the reflectingplane. FIG. 72 is a perspective view showing the model of the crystalgrown layer which was used as the base of calculations. FIG. 73 is adiagram showing the model which was used to calculate the angledependence. FIG. 74 is a diagram showing the dependence of angle onlight emergence efficiency. FIG. 75 is a diagram showing the model whichwas used to calculate the height dependency. FIG. 76 is a diagramshowing the dependence of height on light emergence efficiency.

The simulation is based on the assumption that the crystal grown layerhas the flat C-plane at its top and also has the active layer which isnot parallel to the principal plane of the substrate for growth. Thisassumption does not differ essentially from the actual one in lightemergence efficiency. The angle dependence was simulated on thefollowing assumption, as shown in FIG. 73. The sapphire substrate has arefractive index of n equal to 1.65. The active layer is 20 μm wide andis formed 5 μm above the substrate. The crystal grown layer has arefractive index of n equal to 2.4. The reflecting plane has areflectivity of 70% and is formed at a height of 10 μm. On the basis ofthis assumption, the angle of reflection by the reflecting plane wascalculated. The results are shown in FIG. 74. It is noted thatimprovement in light emergence efficiency is achieved in the range ofabout 50° to about 90°, with better results near about 50°.

The height dependence was simulated on the following assumption, asshown in FIG. 75. The sapphire substrate has a refractive index of nequal to 1.65. The active layer is 20 μm wide and is formed d/2 μm abovethe substrate. The crystal grown layer has a refractive index of n equalto 2.4. The reflecting plane has a reflectivity of 70%. The reflectingplane (S-plane) is formed at an angle of 62°. The results are shown inFIG. 76. It is noted that light emergence efficiency is improved as theheight d increases. The results of the simulations shown in FIGS. 74 and76 suggest that light emergence efficiency is improved as the angle θ ofthe side face is decreased and as the aspect ratio (the ratio of heightd to the width of the device) is increased. In other words, the smallerthe device size, the shorter the time required for crystal growth, andthe smaller the device size, the more significant the effect.

The semiconductor light-emitting device in this example is characterizedin that part of light generated in it emerges after reflection by thereflecting plane 240 which is parallel to the slant crystal plane. Sincereflection by the reflecting plane 240 improves the emergenceefficiency, the semiconductor light-emitting device has increasedbrightness. Moreover, the reflecting plane 240 is formed on the slantcrystal plane which can be readily formed by itself by selective growthwithout additional etching.

The light-emitting device constructed as shown in FIG. 70 offers anadvantage that, in addition to the effect produced by the increased areaof the active layer, the S-plane slanting to the principal plane of thesubstrate increases the number of bonds from nitrogen atoms to galliumatoms, thereby increasing the effective V/III ratio. Therefore, theresulting light-emitting device has improved performance. In addition,it is believe that dislocations extending from the substrate can bendthereby decreasing defects. The slant crystal plane slanting to theprincipal plane of the substrate prevents multiple reflection, therebypermitting the generated light to emerge efficiently. The structure inwhich the active layers 226 are isolated or separated from one anotherwhich obviates the necessity of etching the active layer 226, therebyeliminating damages to the active layer. Another advantage is that theeffective area of the active layer 226 is not reduced by the electrode.

Example 20

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 254 on the substrate for growth 250 takes theshape of a stripe, as shown in FIG. 77. The device includes thesubstrate for growth 250, the underlying layer for growth 251, themasking layer 252, and the crystal grown layer 254 formed in the windowregion in the masking layer 252. The crystal grown layer 254 has theslant side face 256 as the S-plane, on which the active layer 255 isformed. The light generated by the device is reflected by the reflectingplane parallel to the S-plane, which improves light emergenceefficiency. Therefore, the semiconductor light-emitting device has highbrightness and the slant crystal grown layer as the base of thereflecting plane is readily formed by selective growth. Thus, the deviceeffectively relieves brightness saturation and improves devicereliability.

Example 21

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 264 on the substrate for growth 260 takes theshape of an elongated prismoid, as shown in FIG. 78. The device includesthe substrate for growth 260, the underlying layer for growth 261, themasking layer 262, and the crystal grown layer 264 formed in the windowregion in the masking layer 262. The crystal grown layer 264 has theslant side face 263S as the S-plane, the longitudinal end face 264 asthe (11–22) plane, and the top face 263C as the C-plane (which isidentical to the principal plane of the substrate). The active layer(which is not shown) is formed on the slant side face 263S, the end face264, and the top face 263C. The light generated by the device isreflected by the reflecting plane parallel to the S-plane, whichimproves light emergence efficiency. Therefore, the semiconductorlight-emitting device has high brightness and the slant crystal grownlayer as the base of the reflecting plane is readily formed by selectivegrowth. Thus, the device effectively relieves brightness saturation andimproves device reliability.

Example 22

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 274 on the substrate for growth 270 takes theshape of a quadrangular prismoid, as shown in FIG. 79. The deviceincludes the substrate for growth 270, the underlying layer for growth271 formed thereon, the masking layer 272, and the crystal grown layer273 formed in the window region in the masking layer 272. Thequadrangular prismoids are arranged in a matrix. The crystal grown layer273 (in the shape of a quadrangular prismoid) has the slant side face273S as the S-plane, another slant side face 274 as the (11–22) plane,and the top face 2753C as the C-plane (which is identical to theprincipal plane of the substrate). The active layer (which is not shown)is formed on the slant side face 273S, another face 274, and the topface 273C. The light generated by the device is reflected by thereflecting plane parallel to the S-plane, which improves light emergenceefficiency. Therefore, the semiconductor light-emitting device has highbrightness and the slant crystal grown layer as the base of thereflecting plane is readily formed by selective growth. Thus, the deviceeffectively relieves brightness saturation and improves devicereliability.

Example 23

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 283 on the substrate for growth 280 takes theshape of a hexagonal pyramid, as shown in FIG. 80. The device includesthe substrate for growth 280, the underlying layer for growth 281 formedthereon, the masking layer 282, and the crystal grown layer 283 formedin the window region in the masking layer 282. The hexagonal pyramidsare arranged in a matrix. The crystal grown layer 283 (in the shape of ahexagonal pyramid) has the slant side faces as the S-plane. Thehexagonal pyramid has the cross section as shown in FIG. 69. The activelayer (which is not shown) is formed on the slant S-plane. The lightgenerated by the device is reflected by the reflecting plane parallel tothe S-plane, which improves light emergence efficiency. Therefore, thesemiconductor light-emitting device has high brightness and the slantcrystal grown layer as the base of the reflecting plane is readilyformed by selective growth. Thus, the device effectively relievesbrightness saturation and improves device reliability.

Example 24

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layer 293 on the substrate for growth 290 takes theshape of a hexagonal prismoid, as shown in FIG. 81. The device includesthe substrate for growth 290, the underlying layer for growth 291 formedthereon, the masking layer 292, and the crystal grown layer 293 formedin the window region in the masking layer 292. The hexagonal prismoidsare arranged in a matrix pattern. The crystal grown layer 293 (in theshape of a hexagonal prismoid) has the slant side faces 293S as theS-plane and the top face 293C as the C-plane which is identical with theprincipal plane of the substrate. The base of the hexagonal prismoid isthe M-plane or the (1–100) plane, which is formed low (i.e., near thebase of the hexagonal prismoid). The hexagonal prismoid has the crosssection as shown in FIG. 69. The active layer (which is not shown) isformed on the slant S-plane and the C-plane. The light generated by thedevice is reflected by the reflecting plane parallel to the S-plane,which improves light emergence efficiency. Therefore, the semiconductorlight-emitting device has high brightness and the slant crystal grownlayer as the base of the reflecting plane is readily formed by selectivegrowth. Thus, the device effectively relieves brightness saturation andimproves device reliability.

Example 25

This example demonstrates a semiconductor light-emitting device in whichthe crystal grown layers 298 and 299 on the substrate for growth 295take respectively the shape of a hexagonal pyramid and a quadrangularprismoid, as shown in FIG. 82. The device includes the substrate forgrowth 295, the underlying layer for growth 296 formed thereon, themasking layer 297, and the crystal grown layers 298 and 299 formed inthe window region in the masking layer 297. The crystal grown layer 298takes the shape of a hexagonal pyramid, and the crystal grown layer 299takes the shape of a quadrangular prismoid. The hexagonal pyramids andquadrangular prismoids are arranged in a matrix, and they are arrangedin line alternately.

The crystal grown layer 299 (in the shape of a quadrangular prismoid)has the slant side faces 299S as the S-plane, another slant faces 229Zas the (11–22) plane, and the top face 299C as the C-plane which isidentical to the principal plane of the substrate. The crystal grownlayer 298 (in the shape of a hexagonal pyramid) has the slant side faces298S as the S-plane. The hexagonal pyramid has the cross section asshown in FIG. 69. The active layer (which is not shown) is formed on theslant S-plane and the C-plane. The light generated by the device isreflected by the reflecting plane parallel to the S-plane, whichimproves light emergence efficiency. Therefore, the semiconductorlight-emitting device has high brightness and the slant crystal grownlayer as the base of the reflecting plane is readily formed by selectivegrowth. Thus, the device effectively relieves brightness saturation andimproves device reliability.

Example 26

This example demonstrates a process for producing the above-mentionedsemiconductor light-emitting device. The process will be described withreference to FIGS. 83 to 88.

First, on a substrate for growth 300 such as a sapphire substrate then-type GaN layer 301 is formed by MOCVD or the like as an underlyinglayer for growth, as shown in FIG. 83. The n-type GaN layer 301 needsnot be n-type initially. However, it is acceptable so long as itsuppermost surface is n-type. The desired n-type GaN layer 301 may beformed by doping with silicon, for instance.

Then, on the entire surface of the n-type GaN layer 301 the maskinglayer 302 is formed by CVD as a growth inhibiting film, such as asilicon oxide film, a silicon nitride film, a tungsten film, and thelike. In the masking layer 302, the hexagonal window region 303, inwhich the device will be formed, is formed, as shown in FIG. 84.

Subsequently, selective growth is carried out such that the n-type(Al)GaN layer 304 (as the crystal grown layer) is grown from the windowregion 303. This n-type (Al)GaN layer 304, which takes the shape of anapproximately hexagonal pyramid, functions also as a cladding layer. Theslant side face is the S-plane.

On the slant side face, the InGaN layer 305 (as an active layer) and thep-type (Al)GaN layer 306, are formed as shown in FIG. 86. The InGaNlayer 305 as an active layer extends broadly over the S-plane of the(Al)GaN layer 304 as the crystal grown layer, not parallel to theprincipal plane of the substrate for growth. The area S of the activelayer is larger than the area of the window region 303 and the projectedarea of the crystal grown layer, and is formed with sufficient expanse.It is possible to form an AlGaN cap layer on the InGaN layer 305. Theslant crystal face of the p-type (Al)GaN layer 306 functions as thereflecting plane.

Where poly-GaN is grown on the masking layer, unnecessary parts areremoved by etching. The masking layer 302 is removed partly or entirelyto form the n-side contact region 307, as shown in FIG. 87. Thep-electrode 309 of Ni/Pt/Au is formed by vapor deposition or the like.The n-electrode 308 of Ti/Al/Pt/Au is formed in the contact region 307by lift-off technique or the like (FIG. 88). After alloying, the deviceon the substrate is completed. Since the p-electrode 309 is formed onthe p-type (Al)GaN layer 306 which functions as a reflecting plane or areflecting region, it also functions as a reflecting film and alight-shielding film.

The individual devices are so small that it is difficult to separatethem from one another. However, it is only necessary to separate theminto groups by dicing, cleavage, or the like, each group includingdevices arranged in one dimension or two dimensions. Individual devicesin each group may or may not be driven independently. The GaN crystalsgrown on the sapphire substrate can be peeled off from the sapphiresubstrate if the sapphire/GaN interface is subjected to UV laserabrasion through the sapphire, as reported by W. S. Wong et al. inAPL-75-10, 1360-2. If the first grown film (the first conductive film)is removed by etching before or after laser abrasion, it is possible toform a single semiconductor light-emitting device having the basicstructure according to an embodiment of the present invention.

As mentioned above, the process in this example offers an advantage thatthe S-plane can be formed easily by selective growth and the activelayer can be formed on the crystal grown layer whose side face is theS-plane. Thus, it is possible to form the reflecting plane by itself.The light generated by the device is partly reflected by the reflectingplane parallel to the slant crystal plane formed by selective growth.This reflection improves light emergence efficiency and hence, thesemiconductor light-emitting device has high brightness.

Example 27

This example demonstrates a semiconductor light-emitting device havingthe structure as shown in FIG. 89. The device includes the substrate forgrowth 310, the second grown layer 311 formed partly thereon, the firstconductive layer 311 (covering the second grown layer 311), the activelayer 313, and the second conductive layer 319. Although there is not amasking layer or window regions, the area of the active layer 313 islarger than the projected area of the crystal grown layer, therebyeffectively relieving brightness saturation and improving devicereliability.

In other words, even if a growth inhibiting film (such as a maskinglayer) is not used, it is possible to form a stable surface and producethe same effect as that which would be obtained by forming a growthinhibiting film, if microfabrication is carried out by etching (forexample, surface irregularities are formed on the substrate for growthor the crystal film which has been grown previously).

Additionally, according to an embodiment of the present invention, ahexagonal opening is most desirable as the window region in which thehexagonal pyramid is grown. However, the shape of the opening or thedirection of the boundary of the opening is arbitrary because the stableplane is eventually formed by itself even with growth through a roundopening. The present invention is applicable also to the structure inwhich the stable plane, such as the (11–22) plane and the (1–100) planeother than the (1–101) plane in a wurtzite crystal, is formed by itself.

At present, red LEDs are usually made from an AlGaInP compound ofzincblende structure. This compound has stable planes such as the (011)plane and the (111) plane with respect to the (001) substrate. If it isgrown under adequate conditions, it is possible to form the stable planeand the active layer thereon.

The advantage of the semiconductor light-emitting device and itsproduction process according to an embodiment of the present inventionis that it is possible to increase the effective V/III ratio byutilizing the slant crystal plane slanting to the principal plane of thesubstrate. This permits more atoms constituting the compound crystal tobe taken up and decreases the fluctuation of light emission. Moreover,it is possible to suppress the dissociation of nitrogen atoms andimprove crystal properties, thereby decreasing the density of pointdefects. This prevents brightness from becoming saturated when thelight-emitting device is supplied with a strong current. The slantcrystal plane slanting to the principal plane of the substrate preventsmultiple reflection and hence, permits the generated light to emergeefficiently.

The selective growth to form the crystal layer as the slant crystalplane (such as the S-plane) gives minute devices in a small range. Thus,it is possible to densely arrange the devices or to separate the devicesfrom one another by dicing or the like. Part of the stable planeresulting from selective growth is flat on the atomic scale; it has nofluctuation in brightness and it permits light emission with a narrowhalf width. Therefore, this plane can be applied to semiconductorlight-emitting diodes as well as semiconductor lasers.

The semiconductor light-emitting device according to an embodiment ofthe present invention is characterized in that part of light emergingfrom it is one which has been reflected by the reflecting plane which isformed by selective growth parallel to the slant crystal plane.Reflection improves light emergence efficiency and hence, thesemiconductor light-emitting device has high brightness. The slantcrystal layer as the base of the reflecting plane is readily formed byselective growth without additional production steps such as etching.Moreover, the active layer parallel to the slant crystal plane has alarge effective area, which leads to reduced resistance, reduced heatgeneration, and improved reliability. With a large effective area, theactive layer has a reduced load per unit area, which contributes to highbrightness and high reliability. This produces its pronounced effect inthe case of miniaturized devices. The semiconductor light-emittingdevice of the present invention is characterized by the large areapossessed by the active layer, conductive layer, and electrode. Theslant crystal plane helps improve the light emergence efficiency.

One feature of the semiconductor light-emitting device and itsproduction process according to an embodiment of the present inventionis that the cladding layer of a first conductivity type, the activelayer, and the cladding layer of a second conductivity type partly orentirely extend to the masking layer around the opening. An advantage ofthis structure (with the masking layer remaining) is that the laterallygrown part is held by a support which does not disappear. Moreover, themasking layer relieves steps due to the selectively grown structure. Themasking layer, functioning as a supporting layer of the first grownlayer, also keeps the p-electrode and the n-electrode apart withcertainty, thereby preventing short-circuiting, even when the substrateis stripped off by laser irradiation.

The semiconductor light-emitting device of the present invention may beconstructed such that the cladding layer of a first conductivity type,the active layer, and the cladding layer of a second conductivity typeentirely cover the second grown layer and the ends of the cladding layerof a first conductivity type, the active layer, and the cladding layerof a second conductivity type come into direct contact with the maskinglayer. This structure protects the active layer from oxidation and otherdeterioration and also produces an effect of increasing the lightemission area.

An advantage of the semiconductor light-emitting device according to anembodiment of the present invention is that the selective growth to formthe crystal layer as the slant crystal plane gives minute devices in asmall range. Thus it is possible to densely arrange the devices or toseparate the devices from one another by dicing or the like. Part of thestable plane resulting from selective growth is flat on the atomicscale; it has no fluctuation in brightness and it permits light emissionwith a narrow half width. Therefore, this plane can be applied tosemiconductor light-emitting diodes as well as semiconductor lasers.

Another advantage of the semiconductor light-emitting device of thepresent invention is that the active layer has a large effective area,which leads to reduced resistance, reduced heat generation, and improvedreliability. With a large effective area, the active layer has a reducedload per unit area, which contributes to high brightness and highreliability. This produces its pronounced effect in the case ofminiaturized devices. The semiconductor light-emitting device of thepresent invention is characterized by the large area possessed by theactive layer, conductive layer, and electrode. The slant crystal planehelps improve the light emergence efficiency.

Although the present invention has been described with reference tospecific embodiments, those of skill in the art will recognize thatchanges may be made thereto without departing from the spirit and scopeof the invention as set forth in the hereafter appended claims.

1. A lighting system comprising: a plurality of semiconductorlight-emitting device arranged so as to emit light in response to asignal, each of the semiconductor light-emitting devices comprising asubstrate including a substrate surface positioned along a substratesurface plane, a crystal layer comprising an approximately hexagonalprismoid, having a face oriented about an S-plane, and a top regionoriented about a C-plane, and a layer of a first conductivity type, anactive layer, and a layer of a second conductivity type each formedalong at least a portion of the approximately hexagonal prismoid.